List::AllUtils(3pm) User Contributed Perl Documentation List::AllUtils(3pm)
NAME
List::AllUtils - Combines List::Util, List::SomeUtils and List::UtilsBy
in one bite-sized package
VERSION
version 0.19
SYNOPSIS
use List::AllUtils qw( first any );
# _Everything_ from List::Util, List::SomeUtils, and List::UtilsBy
use List::AllUtils qw( :all );
my @numbers = ( 1, 2, 3, 5, 7 );
# or don't import anything
return List::AllUtils::first { $_ > 5 } @numbers;
DESCRIPTION
Are you sick of trying to remember whether a particular helper is
defined in List::Util, List::SomeUtils or List::UtilsBy? I sure am. Now
you don't have to remember. This module will export all of the
functions that either of those three modules defines.
Note that all function documentation has been shamelessly copied from
List::Util, List::SomeUtils and List::UtilsBy.
Which One Wins?
Recently, List::Util has started including some of the subs that used
to only be in List::SomeUtils. Similarly, List::SomeUtils has some
small overlap with List::UtilsBy.
"List::AllUtils" use to always favors the subroutine provided by
List::Util, List::SomeUtils or List::UtilsBy in that order. However, as
of List::Util 1.56, it included some functions, "mesh" and "zip" with
the same name as List::SomeUtils functions, but different behavior.
So going forward, we will always prefer backwards compatibility. This
means that "mesh" and "zip" will always come from List::SomeUtils. If
other incompatible functions are added to List::Util, those will also
be skipped in favor of the List::SomeUtils version.
The docs below come from List::Util 1.56, List::SomeUtils 0.58, and
List::UtilsBy 0.11.
WHAT IS EXPORTED?
All this module does is load List::Util, List::SomeUtils, and
List::UtilsBy, and then re-export everything that they provide. That
means that regardless of the documentation below, you will get any
subroutine that your installed version provides.
LIST-REDUCTION FUNCTIONS
The following set of functions all apply a given block of code to a
list of values.
reduce
$result = reduce { BLOCK } @list
Reduces @list by calling "BLOCK" in a scalar context multiple times,
setting $a and $b each time. The first call will be with $a and $b set
to the first two elements of the list, subsequent calls will be done by
setting $a to the result of the previous call and $b to the next
element in the list.
Returns the result of the last call to the "BLOCK". If @list is empty
then "undef" is returned. If @list only contains one element then that
element is returned and "BLOCK" is not executed.
The following examples all demonstrate how "reduce" could be used to
implement the other list-reduction functions in this module. (They are
not in fact implemented like this, but instead in a more efficient
manner in individual C functions).
$foo = reduce { defined($a) ? $a :
$code->(local $_ = $b) ? $b :
undef } undef, @list # first
$foo = reduce { $a > $b ? $a : $b } 1..10 # max
$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z' # maxstr
$foo = reduce { $a < $b ? $a : $b } 1..10 # min
$foo = reduce { $a lt $b ? $a : $b } 'aa'..'zz' # minstr
$foo = reduce { $a + $b } 1 .. 10 # sum
$foo = reduce { $a . $b } @bar # concat
$foo = reduce { $a || $code->(local $_ = $b) } 0, @bar # any
$foo = reduce { $a && $code->(local $_ = $b) } 1, @bar # all
$foo = reduce { $a && !$code->(local $_ = $b) } 1, @bar # none
$foo = reduce { $a || !$code->(local $_ = $b) } 0, @bar # notall
# Note that these implementations do not fully short-circuit
If your algorithm requires that "reduce" produce an identity value,
then make sure that you always pass that identity value as the first
argument to prevent "undef" being returned
$foo = reduce { $a + $b } 0, @values; # sum with 0 identity value
The above example code blocks also suggest how to use "reduce" to build
a more efficient combined version of one of these basic functions and a
"map" block. For example, to find the total length of all the strings
in a list, we could use
$total = sum map { length } @strings;
However, this produces a list of temporary integer values as long as
the original list of strings, only to reduce it down to a single value
again. We can compute the same result more efficiently by using
"reduce" with a code block that accumulates lengths by writing this
instead as:
$total = reduce { $a + length $b } 0, @strings
The other scalar-returning list reduction functions are all
specialisations of this generic idea.
reductions
@results = reductions { BLOCK } @list
Since version 1.54.
Similar to "reduce" except that it also returns the intermediate values
along with the final result. As before, $a is set to the first element
of the given list, and the "BLOCK" is then called once for remaining
item in the list set into $b, with the result being captured for return
as well as becoming the new value for $a.
The returned list will begin with the initial value for $a, followed by
each return value from the block in order. The final value of the
result will be identical to what the "reduce" function would have
returned given the same block and list.
reduce { "$a-$b" } "a".."d" # "a-b-c-d"
reductions { "$a-$b" } "a".."d" # "a", "a-b", "a-b-c", "a-b-c-d"
any
my $bool = any { BLOCK } @list;
Since version 1.33.
Similar to "grep" in that it evaluates "BLOCK" setting $_ to each
element of @list in turn. "any" returns true if any element makes the
"BLOCK" return a true value. If "BLOCK" never returns true or @list was
empty then it returns false.
Many cases of using "grep" in a conditional can be written using "any"
instead, as it can short-circuit after the first true result.
if( any { length > 10 } @strings ) {
# at least one string has more than 10 characters
}
Note: Due to XS issues the block passed may be able to access the outer
@_ directly. This is not intentional and will break under debugger.
all
my $bool = all { BLOCK } @list;
Since version 1.33.
Similar to "any", except that it requires all elements of the @list to
make the "BLOCK" return true. If any element returns false, then it
returns false. If the "BLOCK" never returns false or the @list was
empty then it returns true.
Note: Due to XS issues the block passed may be able to access the outer
@_ directly. This is not intentional and will break under debugger.
none
notall
my $bool = none { BLOCK } @list;
my $bool = notall { BLOCK } @list;
Since version 1.33.
Similar to "any" and "all", but with the return sense inverted. "none"
returns true only if no value in the @list causes the "BLOCK" to return
true, and "notall" returns true only if not all of the values do.
Note: Due to XS issues the block passed may be able to access the outer
@_ directly. This is not intentional and will break under debugger.
first
my $val = first { BLOCK } @list;
Similar to "grep" in that it evaluates "BLOCK" setting $_ to each
element of @list in turn. "first" returns the first element where the
result from "BLOCK" is a true value. If "BLOCK" never returns true or
@list was empty then "undef" is returned.
$foo = first { defined($_) } @list # first defined value in @list
$foo = first { $_ > $value } @list # first value in @list which
# is greater than $value
max
my $num = max @list;
Returns the entry in the list with the highest numerical value. If the
list is empty then "undef" is returned.
$foo = max 1..10 # 10
$foo = max 3,9,12 # 12
$foo = max @bar, @baz # whatever
maxstr
my $str = maxstr @list;
Similar to "max", but treats all the entries in the list as strings and
returns the highest string as defined by the "gt" operator. If the list
is empty then "undef" is returned.
$foo = maxstr 'A'..'Z' # 'Z'
$foo = maxstr "hello","world" # "world"
$foo = maxstr @bar, @baz # whatever
min
my $num = min @list;
Similar to "max" but returns the entry in the list with the lowest
numerical value. If the list is empty then "undef" is returned.
$foo = min 1..10 # 1
$foo = min 3,9,12 # 3
$foo = min @bar, @baz # whatever
minstr
my $str = minstr @list;
Similar to "min", but treats all the entries in the list as strings and
returns the lowest string as defined by the "lt" operator. If the list
is empty then "undef" is returned.
$foo = minstr 'A'..'Z' # 'A'
$foo = minstr "hello","world" # "hello"
$foo = minstr @bar, @baz # whatever
product
my $num = product @list;
Since version 1.35.
Returns the numerical product of all the elements in @list. If @list is
empty then 1 is returned.
$foo = product 1..10 # 3628800
$foo = product 3,9,12 # 324
sum
my $num_or_undef = sum @list;
Returns the numerical sum of all the elements in @list. For backwards
compatibility, if @list is empty then "undef" is returned.
$foo = sum 1..10 # 55
$foo = sum 3,9,12 # 24
$foo = sum @bar, @baz # whatever
sum0
my $num = sum0 @list;
Since version 1.26.
Similar to "sum", except this returns 0 when given an empty list,
rather than "undef".
KEY/VALUE PAIR LIST FUNCTIONS
The following set of functions, all inspired by List::Pairwise, consume
an even-sized list of pairs. The pairs may be key/value associations
from a hash, or just a list of values. The functions will all preserve
the original ordering of the pairs, and will not be confused by
multiple pairs having the same "key" value - nor even do they require
that the first of each pair be a plain string.
NOTE: At the time of writing, the following "pair*" functions that take
a block do not modify the value of $_ within the block, and instead
operate using the $a and $b globals instead. This has turned out to be
a poor design, as it precludes the ability to provide a "pairsort"
function. Better would be to pass pair-like objects as 2-element array
references in $_, in a style similar to the return value of the "pairs"
function. At some future version this behaviour may be added.
Until then, users are alerted NOT to rely on the value of $_ remaining
unmodified between the outside and the inside of the control block. In
particular, the following example is UNSAFE:
my @kvlist = ...
foreach (qw( some keys here )) {
my @items = pairgrep { $a eq $_ } @kvlist;
...
}
Instead, write this using a lexical variable:
foreach my $key (qw( some keys here )) {
my @items = pairgrep { $a eq $key } @kvlist;
...
}
pairs
my @pairs = pairs @kvlist;
Since version 1.29.
A convenient shortcut to operating on even-sized lists of pairs, this
function returns a list of "ARRAY" references, each containing two
items from the given list. It is a more efficient version of
@pairs = pairmap { [ $a, $b ] } @kvlist
It is most convenient to use in a "foreach" loop, for example:
foreach my $pair ( pairs @kvlist ) {
my ( $key, $value ) = @$pair;
...
}
Since version 1.39 these "ARRAY" references are blessed objects,
recognising the two methods "key" and "value". The following code is
equivalent:
foreach my $pair ( pairs @kvlist ) {
my $key = $pair->key;
my $value = $pair->value;
...
}
Since version 1.51 they also have a "TO_JSON" method to ease
serialisation.
unpairs
my @kvlist = unpairs @pairs
Since version 1.42.
The inverse function to "pairs"; this function takes a list of "ARRAY"
references containing two elements each, and returns a flattened list
of the two values from each of the pairs, in order. This is notionally
equivalent to
my @kvlist = map { @{$_}[0,1] } @pairs
except that it is implemented more efficiently internally.
Specifically, for any input item it will extract exactly two values for
the output list; using "undef" if the input array references are short.
Between "pairs" and "unpairs", a higher-order list function can be used
to operate on the pairs as single scalars; such as the following near-
equivalents of the other "pair*" higher-order functions:
@kvlist = unpairs grep { FUNC } pairs @kvlist
# Like pairgrep, but takes $_ instead of $a and $b
@kvlist = unpairs map { FUNC } pairs @kvlist
# Like pairmap, but takes $_ instead of $a and $b
Note however that these versions will not behave as nicely in scalar
context.
Finally, this technique can be used to implement a sort on a keyvalue
pair list; e.g.:
@kvlist = unpairs sort { $a->key cmp $b->key } pairs @kvlist
pairkeys
my @keys = pairkeys @kvlist;
Since version 1.29.
A convenient shortcut to operating on even-sized lists of pairs, this
function returns a list of the the first values of each of the pairs in
the given list. It is a more efficient version of
@keys = pairmap { $a } @kvlist
pairvalues
my @values = pairvalues @kvlist;
Since version 1.29.
A convenient shortcut to operating on even-sized lists of pairs, this
function returns a list of the the second values of each of the pairs
in the given list. It is a more efficient version of
@values = pairmap { $b } @kvlist
pairgrep
my @kvlist = pairgrep { BLOCK } @kvlist;
my $count = pairgrep { BLOCK } @kvlist;
Since version 1.29.
Similar to perl's "grep" keyword, but interprets the given list as an
even-sized list of pairs. It invokes the "BLOCK" multiple times, in
scalar context, with $a and $b set to successive pairs of values from
the @kvlist.
Returns an even-sized list of those pairs for which the "BLOCK"
returned true in list context, or the count of the number of pairs in
scalar context. (Note, therefore, in scalar context that it returns a
number half the size of the count of items it would have returned in
list context).
@subset = pairgrep { $a =~ m/^[[:upper:]]+$/ } @kvlist
As with "grep" aliasing $_ to list elements, "pairgrep" aliases $a and
$b to elements of the given list. Any modifications of it by the code
block will be visible to the caller.
pairfirst
my ( $key, $val ) = pairfirst { BLOCK } @kvlist;
my $found = pairfirst { BLOCK } @kvlist;
Since version 1.30.
Similar to the "first" function, but interprets the given list as an
even-sized list of pairs. It invokes the "BLOCK" multiple times, in
scalar context, with $a and $b set to successive pairs of values from
the @kvlist.
Returns the first pair of values from the list for which the "BLOCK"
returned true in list context, or an empty list of no such pair was
found. In scalar context it returns a simple boolean value, rather than
either the key or the value found.
( $key, $value ) = pairfirst { $a =~ m/^[[:upper:]]+$/ } @kvlist
As with "grep" aliasing $_ to list elements, "pairfirst" aliases $a and
$b to elements of the given list. Any modifications of it by the code
block will be visible to the caller.
pairmap
my @list = pairmap { BLOCK } @kvlist;
my $count = pairmap { BLOCK } @kvlist;
Since version 1.29.
Similar to perl's "map" keyword, but interprets the given list as an
even-sized list of pairs. It invokes the "BLOCK" multiple times, in
list context, with $a and $b set to successive pairs of values from the
@kvlist.
Returns the concatenation of all the values returned by the "BLOCK" in
list context, or the count of the number of items that would have been
returned in scalar context.
@result = pairmap { "The key $a has value $b" } @kvlist
As with "map" aliasing $_ to list elements, "pairmap" aliases $a and $b
to elements of the given list. Any modifications of it by the code
block will be visible to the caller.
See "KNOWN BUGS" for a known-bug with "pairmap", and a workaround.
OTHER FUNCTIONS
shuffle
my @values = shuffle @values;
Returns the values of the input in a random order
@cards = shuffle 0..51 # 0..51 in a random order
This function is affected by the $RAND variable.
sample
my @items = sample $count, @values
Since version 1.54.
Randomly select the given number of elements from the input list. Any
given position in the input list will be selected at most once.
If there are fewer than $count items in the list then the function will
return once all of them have been randomly selected; effectively the
function behaves similarly to "shuffle".
This function is affected by the $RAND variable.
uniq
my @subset = uniq @values
Since version 1.45.
Filters a list of values to remove subsequent duplicates, as judged by
a DWIM-ish string equality or "undef" test. Preserves the order of
unique elements, and retains the first value of any duplicate set.
my $count = uniq @values
In scalar context, returns the number of elements that would have been
returned as a list.
The "undef" value is treated by this function as distinct from the
empty string, and no warning will be produced. It is left as-is in the
returned list. Subsequent "undef" values are still considered identical
to the first, and will be removed.
uniqint
my @subset = uniqint @values
Since version 1.55.
Filters a list of values to remove subsequent duplicates, as judged by
an integer numerical equality test. Preserves the order of unique
elements, and retains the first value of any duplicate set. Values in
the returned list will be coerced into integers.
my $count = uniqint @values
In scalar context, returns the number of elements that would have been
returned as a list.
Note that "undef" is treated much as other numerical operations treat
it; it compares equal to zero but additionally produces a warning if
such warnings are enabled ("use warnings 'uninitialized';"). In
addition, an "undef" in the returned list is coerced into a numerical
zero, so that the entire list of values returned by "uniqint" are well-
behaved as integers.
uniqnum
my @subset = uniqnum @values
Since version 1.44.
Filters a list of values to remove subsequent duplicates, as judged by
a numerical equality test. Preserves the order of unique elements, and
retains the first value of any duplicate set.
my $count = uniqnum @values
In scalar context, returns the number of elements that would have been
returned as a list.
Note that "undef" is treated much as other numerical operations treat
it; it compares equal to zero but additionally produces a warning if
such warnings are enabled ("use warnings 'uninitialized';"). In
addition, an "undef" in the returned list is coerced into a numerical
zero, so that the entire list of values returned by "uniqnum" are well-
behaved as numbers.
Note also that multiple IEEE "NaN" values are treated as duplicates of
each other, regardless of any differences in their payloads, and
despite the fact that "0+'NaN' == 0+'NaN'" yields false.
uniqstr
my @subset = uniqstr @values
Since version 1.45.
Filters a list of values to remove subsequent duplicates, as judged by
a string equality test. Preserves the order of unique elements, and
retains the first value of any duplicate set.
my $count = uniqstr @values
In scalar context, returns the number of elements that would have been
returned as a list.
Note that "undef" is treated much as other string operations treat it;
it compares equal to the empty string but additionally produces a
warning if such warnings are enabled ("use warnings 'uninitialized';").
In addition, an "undef" in the returned list is coerced into an empty
string, so that the entire list of values returned by "uniqstr" are
well-behaved as strings.
head
my @values = head $size, @list;
Since version 1.50.
Returns the first $size elements from @list. If $size is negative,
returns all but the last $size elements from @list.
@result = head 2, qw( foo bar baz );
# foo, bar
@result = head -2, qw( foo bar baz );
# foo
tail
my @values = tail $size, @list;
Since version 1.50.
Returns the last $size elements from @list. If $size is negative,
returns all but the first $size elements from @list.
@result = tail 2, qw( foo bar baz );
# bar, baz
@result = tail -2, qw( foo bar baz );
# baz
List::SomeUtils FUNCTIONS
Junctions
Treatment of an empty list
There are two schools of thought for how to evaluate a junction on an
empty list:
• Reduction to an identity (boolean)
• Result is undefined (three-valued)
In the first case, the result of the junction applied to the empty list
is determined by a mathematical reduction to an identity depending on
whether the underlying comparison is "or" or "and". Conceptually:
"any are true" "all are true"
-------------- --------------
2 elements: A || B || 0 A && B && 1
1 element: A || 0 A && 1
0 elements: 0 1
In the second case, three-value logic is desired, in which a junction
applied to an empty list returns "undef" rather than true or false
Junctions with a "_u" suffix implement three-valued logic. Those
without are boolean.
all BLOCK LIST
all_u BLOCK LIST
Returns a true value if all items in LIST meet the criterion given
through BLOCK. Sets $_ for each item in LIST in turn:
print "All values are non-negative"
if all { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "all" returns true (i.e. no values failed the
condition) and "all_u" returns "undef".
Thus, "all_u(@list)" is equivalent to "@list ? all(@list) : undef".
Note: because Perl treats "undef" as false, you must check the return
value of "all_u" with "defined" or you will get the opposite result of
what you expect.
any BLOCK LIST
any_u BLOCK LIST
Returns a true value if any item in LIST meets the criterion given
through BLOCK. Sets $_ for each item in LIST in turn:
print "At least one non-negative value"
if any { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "any" returns false and "any_u" returns "undef".
Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
none BLOCK LIST
none_u BLOCK LIST
Logically the negation of "any". Returns a true value if no item in
LIST meets the criterion given through BLOCK. Sets $_ for each item in
LIST in turn:
print "No non-negative values"
if none { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "none" returns true (i.e. no values failed the
condition) and "none_u" returns "undef".
Thus, "none_u(@list)" is equivalent to "@list ? none(@list) : undef".
Note: because Perl treats "undef" as false, you must check the return
value of "none_u" with "defined" or you will get the opposite result of
what you expect.
notall BLOCK LIST
notall_u BLOCK LIST
Logically the negation of "all". Returns a true value if not all items
in LIST meet the criterion given through BLOCK. Sets $_ for each item
in LIST in turn:
print "Not all values are non-negative"
if notall { $_ >= 0 } ($x, $y, $z);
For an empty LIST, "notall" returns false and "notall_u" returns
"undef".
Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) :
undef".
one BLOCK LIST
one_u BLOCK LIST
Returns a true value if precisely one item in LIST meets the criterion
given through BLOCK. Sets $_ for each item in LIST in turn:
print "Precisely one value defined"
if one { defined($_) } @list;
Returns false otherwise.
For an empty LIST, "one" returns false and "one_u" returns "undef".
The expression "one BLOCK LIST" is almost equivalent to "1 == true
BLOCK LIST", except for short-cutting. Evaluation of BLOCK will
immediately stop at the second true value.
Transformation
apply BLOCK LIST
Makes a copy of the list and then passes each element from the copy to
the BLOCK. Any changes or assignments to $_ in the BLOCK will only
affect the elements of the new list. However, if $_ is a reference then
changes to the referenced value will be seen in both the original and
new list.
This function is similar to "map" but will not modify the elements of
the input list:
my @list = (1 .. 4);
my @mult = apply { $_ *= 2 } @list;
print "\@list = @list\n";
print "\@mult = @mult\n";
__END__
@list = 1 2 3 4
@mult = 2 4 6 8
Think of it as syntactic sugar for
for (my @mult = @list) { $_ *= 2 }
Note that you must alter $_ directly inside BLOCK in order for changes
to make effect. New value returned from the BLOCK are ignored:
# @new is identical to @list.
my @new = apply { $_ * 2 } @list;
# @new is different from @list
my @new = apply { $_ =* 2 } @list;
insert_after BLOCK VALUE LIST
Inserts VALUE after the first item in LIST for which the criterion in
BLOCK is true. Sets $_ for each item in LIST in turn.
my @list = qw/This is a list/;
insert_after { $_ eq "a" } "longer" => @list;
print "@list";
__END__
This is a longer list
insert_after_string STRING VALUE LIST
Inserts VALUE after the first item in LIST which is equal to STRING.
my @list = qw/This is a list/;
insert_after_string "a", "longer" => @list;
print "@list";
__END__
This is a longer list
pairwise BLOCK ARRAY1 ARRAY2
Evaluates BLOCK for each pair of elements in ARRAY1 and ARRAY2 and
returns a new list consisting of BLOCK's return values. The two
elements are set to $a and $b. Note that those two are aliases to the
original value so changing them will modify the input arrays.
@a = (1 .. 5);
@b = (11 .. 15);
@x = pairwise { $a + $b } @a, @b; # returns 12, 14, 16, 18, 20
# mesh with pairwise
@a = qw/a b c/;
@b = qw/1 2 3/;
@x = pairwise { ($a, $b) } @a, @b; # returns a, 1, b, 2, c, 3
mesh ARRAY1 ARRAY2 [ ARRAY3 ... ]
zip ARRAY1 ARRAY2 [ ARRAY3 ... ]
Returns a list consisting of the first elements of each array, then the
second, then the third, etc, until all arrays are exhausted.
Examples:
@x = qw/a b c d/;
@y = qw/1 2 3 4/;
@z = mesh @x, @y; # returns a, 1, b, 2, c, 3, d, 4
@a = ('x');
@b = ('1', '2');
@c = qw/zip zap zot/;
@d = mesh @a, @b, @c; # x, 1, zip, undef, 2, zap, undef, undef, zot
"zip" is an alias for "mesh".
uniq LIST
distinct LIST
Returns a new list by stripping duplicate values in LIST by comparing
the values as hash keys, except that undef is considered separate from
''. The order of elements in the returned list is the same as in LIST.
In scalar context, returns the number of unique elements in LIST.
my @x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 1 2 3 5 4
my $x = uniq 1, 1, 2, 2, 3, 5, 3, 4; # returns 5
# returns "Mike", "Michael", "Richard", "Rick"
my @n = distinct "Mike", "Michael", "Richard", "Rick", "Michael", "Rick"
# returns '', undef, 'S1', A5'
my @s = distinct '', undef, 'S1', 'A5'
# returns '', undef, 'S1', A5'
my @w = uniq undef, '', 'S1', 'A5'
"distinct" is an alias for "uniq".
RT#49800 can be used to give feedback about this behavior.
singleton
Returns a new list by stripping values in LIST occurring more than once
by comparing the values as hash keys, except that undef is considered
separate from ''. The order of elements in the returned list is the
same as in LIST. In scalar context, returns the number of elements
occurring only once in LIST.
my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
Partitioning
after BLOCK LIST
Returns a list of the values of LIST after (and not including) the
point where BLOCK returns a true value. Sets $_ for each element in
LIST in turn.
@x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
after_incl BLOCK LIST
Same as "after" but also includes the element for which BLOCK is true.
before BLOCK LIST
Returns a list of values of LIST up to (and not including) the point
where BLOCK returns a true value. Sets $_ for each element in LIST in
turn.
before_incl BLOCK LIST
Same as "before" but also includes the element for which BLOCK is true.
part BLOCK LIST
Partitions LIST based on the return value of BLOCK which denotes into
which partition the current value is put.
Returns a list of the partitions thusly created. Each partition created
is a reference to an array.
my $i = 0;
my @part = part { $i++ % 2 } 1 .. 8; # returns [1, 3, 5, 7], [2, 4, 6, 8]
You can have a sparse list of partitions as well where non-set
partitions will be undef:
my @part = part { 2 } 1 .. 10; # returns undef, undef, [ 1 .. 10 ]
Be careful with negative values, though:
my @part = part { -1 } 1 .. 10;
__END__
Modification of non-creatable array value attempted, subscript -1 ...
Negative values are only ok when they refer to a partition previously
created:
my @idx = ( 0, 1, -1 );
my $i = 0;
my @part = part { $idx[$i++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
Iteration
each_array ARRAY1 ARRAY2 ...
Creates an array iterator to return the elements of the list of arrays
ARRAY1, ARRAY2 throughout ARRAYn in turn. That is, the first time it
is called, it returns the first element of each array. The next time,
it returns the second elements. And so on, until all elements are
exhausted.
This is useful for looping over more than one array at once:
my $ea = each_array(@a, @b, @c);
while ( my ($a, $b, $c) = $ea->() ) { .... }
The iterator returns the empty list when it reached the end of all
arrays.
If the iterator is passed an argument of '"index"', then it returns the
index of the last fetched set of values, as a scalar.
each_arrayref LIST
Like each_array, but the arguments are references to arrays, not the
plain arrays.
natatime EXPR, LIST
Creates an array iterator, for looping over an array in chunks of $n
items at a time. (n at a time, get it?). An example is probably a
better explanation than I could give in words.
Example:
my @x = ('a' .. 'g');
my $it = natatime 3, @x;
while (my @vals = $it->())
{
print "@vals\n";
}
This prints
a b c
d e f
g
Searching
bsearch BLOCK LIST
Performs a binary search on LIST which must be a sorted list of values.
BLOCK must return a negative value if the current element (stored in
$_) is smaller, a positive value if it is bigger and zero if it
matches.
Returns a boolean value in scalar context. In list context, it returns
the element if it was found, otherwise the empty list.
bsearchidx BLOCK LIST
bsearch_index BLOCK LIST
Performs a binary search on LIST which must be a sorted list of values.
BLOCK must return a negative value if the current element (stored in
$_) is smaller, a positive value if it is bigger and zero if it
matches.
Returns the index of found element, otherwise "-1".
"bsearch_index" is an alias for "bsearchidx".
firstval BLOCK LIST
first_value BLOCK LIST
Returns the first element in LIST for which BLOCK evaluates to true.
Each element of LIST is set to $_ in turn. Returns "undef" if no such
element has been found.
"first_value" is an alias for "firstval".
onlyval BLOCK LIST
only_value BLOCK LIST
Returns the only element in LIST for which BLOCK evaluates to true.
Sets $_ for each item in LIST in turn. Returns "undef" if no such
element has been found.
"only_value" is an alias for "onlyval".
lastval BLOCK LIST
last_value BLOCK LIST
Returns the last value in LIST for which BLOCK evaluates to true. Each
element of LIST is set to $_ in turn. Returns "undef" if no such
element has been found.
"last_value" is an alias for "lastval".
firstres BLOCK LIST
first_result BLOCK LIST
Returns the result of BLOCK for the first element in LIST for which
BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
Returns "undef" if no such element has been found.
"first_result" is an alias for "firstres".
onlyres BLOCK LIST
only_result BLOCK LIST
Returns the result of BLOCK for the first element in LIST for which
BLOCK evaluates to true. Sets $_ for each item in LIST in turn. Returns
"undef" if no such element has been found.
"only_result" is an alias for "onlyres".
lastres BLOCK LIST
last_result BLOCK LIST
Returns the result of BLOCK for the last element in LIST for which
BLOCK evaluates to true. Each element of LIST is set to $_ in turn.
Returns "undef" if no such element has been found.
"last_result" is an alias for "lastres".
indexes BLOCK LIST
Evaluates BLOCK for each element in LIST (assigned to $_) and returns a
list of the indices of those elements for which BLOCK returned a true
value. This is just like "grep" only that it returns indices instead of
values:
@x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
firstidx BLOCK LIST
first_index BLOCK LIST
Returns the index of the first element in LIST for which the criterion
in BLOCK is true. Sets $_ for each item in LIST in turn:
my @list = (1, 4, 3, 2, 4, 6);
printf "item with index %i in list is 4", firstidx { $_ == 4 } @list;
__END__
item with index 1 in list is 4
Returns "-1" if no such item could be found.
"first_index" is an alias for "firstidx".
onlyidx BLOCK LIST
only_index BLOCK LIST
Returns the index of the only element in LIST for which the criterion
in BLOCK is true. Sets $_ for each item in LIST in turn:
my @list = (1, 3, 4, 3, 2, 4);
printf "uniqe index of item 2 in list is %i", onlyidx { $_ == 2 } @list;
__END__
unique index of item 2 in list is 4
Returns "-1" if either no such item or more than one of these has been
found.
"only_index" is an alias for "onlyidx".
lastidx BLOCK LIST
last_index BLOCK LIST
Returns the index of the last element in LIST for which the criterion
in BLOCK is true. Sets $_ for each item in LIST in turn:
my @list = (1, 4, 3, 2, 4, 6);
printf "item with index %i in list is 4", lastidx { $_ == 4 } @list;
__END__
item with index 4 in list is 4
Returns "-1" if no such item could be found.
"last_index" is an alias for "lastidx".
Sorting
sort_by BLOCK LIST
Returns the list of values sorted according to the string values
returned by the KEYFUNC block or function. A typical use of this may be
to sort objects according to the string value of some accessor, such as
sort_by { $_->name } @people
The key function is called in scalar context, being passed each value
in turn as both $_ and the only argument in the parameters, @_. The
values are then sorted according to string comparisons on the values
returned. This is equivalent to
sort { $a->name cmp $b->name } @people
except that it guarantees the name accessor will be executed only once
per value. One interesting use-case is to sort strings which may have
numbers embedded in them "naturally", rather than lexically.
sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
This sorts strings by generating sort keys which zero-pad the embedded
numbers to some level (9 digits in this case), helping to ensure the
lexical sort puts them in the correct order.
nsort_by BLOCK LIST
Similar to sort_by but compares its key values numerically.
Counting and calculation
true BLOCK LIST
Counts the number of elements in LIST for which the criterion in BLOCK
is true. Sets $_ for each item in LIST in turn:
printf "%i item(s) are defined", true { defined($_) } @list;
false BLOCK LIST
Counts the number of elements in LIST for which the criterion in BLOCK
is false. Sets $_ for each item in LIST in turn:
printf "%i item(s) are not defined", false { defined($_) } @list;
minmax LIST
Calculates the minimum and maximum of LIST and returns a two element
list with the first element being the minimum and the second the
maximum. Returns the empty list if LIST was empty.
The "minmax" algorithm differs from a naive iteration over the list
where each element is compared to two values being the so far
calculated min and max value in that it only requires 3n/2 - 2
comparisons. Thus it is the most efficient possible algorithm.
However, the Perl implementation of it has some overhead simply due to
the fact that there are more lines of Perl code involved. Therefore,
LIST needs to be fairly big in order for "minmax" to win over a naive
implementation. This limitation does not apply to the XS version.
mode LIST
Calculates the most common items in the list and returns them as a
list. This is effectively done by string comparisons, so references
will be stringified. If they implement string overloading, this will be
used.
If more than one item appears the same number of times in the list, all
such items will be returned. For example, the mode of a unique list is
the list itself.
This function returns a list in list context. In scalar context it
returns a count indicating the number of modes in the list.
List::UtilsBy FUNCTIONS
All functions added since version 0.04 unless otherwise stated, as the
original names for earlier versions were renamed.
sort_by
@vals = sort_by { KEYFUNC } @vals
Returns the list of values sorted according to the string values
returned by the "KEYFUNC" block or function. A typical use of this may
be to sort objects according to the string value of some accessor, such
as
sort_by { $_->name } @people
The key function is called in scalar context, being passed each value
in turn as both $_ and the only argument in the parameters, @_. The
values are then sorted according to string comparisons on the values
returned.
This is equivalent to
sort { $a->name cmp $b->name } @people
except that it guarantees the "name" accessor will be executed only
once per value.
One interesting use-case is to sort strings which may have numbers
embedded in them "naturally", rather than lexically.
sort_by { s/(\d+)/sprintf "%09d", $1/eg; $_ } @strings
This sorts strings by generating sort keys which zero-pad the embedded
numbers to some level (9 digits in this case), helping to ensure the
lexical sort puts them in the correct order.
nsort_by
@vals = nsort_by { KEYFUNC } @vals
Similar to "sort_by" but compares its key values numerically.
rev_sort_by
rev_nsort_by
@vals = rev_sort_by { KEYFUNC } @vals
@vals = rev_nsort_by { KEYFUNC } @vals
Since version 0.06.
Similar to "sort_by" and "nsort_by" but returns the list in the reverse
order. Equivalent to
@vals = reverse sort_by { KEYFUNC } @vals
except that these functions are slightly more efficient because they
avoid the final "reverse" operation.
max_by
$optimal = max_by { KEYFUNC } @vals
@optimal = max_by { KEYFUNC } @vals
Returns the (first) value from @vals that gives the numerically largest
result from the key function.
my $tallest = max_by { $_->height } @people
use File::stat qw( stat );
my $newest = max_by { stat($_)->mtime } @files;
In scalar context, the first maximal value is returned. In list
context, a list of all the maximal values is returned. This may be used
to obtain positions other than the first, if order is significant.
If called on an empty list, an empty list is returned.
For symmetry with the "nsort_by" function, this is also provided under
the name "nmax_by" since it behaves numerically.
min_by
$optimal = min_by { KEYFUNC } @vals
@optimal = min_by { KEYFUNC } @vals
Similar to "max_by" but returns values which give the numerically
smallest result from the key function. Also provided as "nmin_by"
minmax_by
( $minimal, $maximal ) = minmax_by { KEYFUNC } @vals
Since version 0.11.
Similar to calling both "min_by" and "max_by" with the same key
function on the same list. This version is more efficient than calling
the two other functions individually, as it has less work to perform
overall. In the case of ties, only the first optimal element found in
each case is returned. Also provided as "nminmax_by".
uniq_by
@vals = uniq_by { KEYFUNC } @vals
Returns a list of the subset of values for which the key function block
returns unique values. The first value yielding a particular key is
chosen, subsequent values are rejected.
my @some_fruit = uniq_by { $_->colour } @fruit;
To select instead the last value per key, reverse the input list. If
the order of the results is significant, don't forget to reverse the
result as well:
my @some_fruit = reverse uniq_by { $_->colour } reverse @fruit;
Because the values returned by the key function are used as hash keys,
they ought to either be strings, or at least well-behaved as strings
(such as numbers, or object references which overload stringification
in a suitable manner).
partition_by
%parts = partition_by { KEYFUNC } @vals
Returns a key/value list of ARRAY refs containing all the original
values distributed according to the result of the key function block.
Each value will be an ARRAY ref containing all the values which
returned the string from the key function, in their original order.
my %balls_by_colour = partition_by { $_->colour } @balls;
Because the values returned by the key function are used as hash keys,
they ought to either be strings, or at least well-behaved as strings
(such as numbers, or object references which overload stringification
in a suitable manner).
count_by
%counts = count_by { KEYFUNC } @vals
Since version 0.07.
Returns a key/value list of integers, giving the number of times the
key function block returned the key, for each value in the list.
my %count_of_balls = count_by { $_->colour } @balls;
Because the values returned by the key function are used as hash keys,
they ought to either be strings, or at least well-behaved as strings
(such as numbers, or object references which overload stringification
in a suitable manner).
zip_by
@vals = zip_by { ITEMFUNC } \@arr0, \@arr1, \@arr2,...
Returns a list of each of the values returned by the function block,
when invoked with values from across each each of the given ARRAY
references. Each value in the returned list will be the result of the
function having been invoked with arguments at that position, from
across each of the arrays given.
my @transposition = zip_by { [ @_ ] } @matrix;
my @names = zip_by { "$_[1], $_[0]" } \@firstnames, \@surnames;
print zip_by { "$_[0] => $_[1]\n" } [ keys %hash ], [ values %hash ];
If some of the arrays are shorter than others, the function will behave
as if they had "undef" in the trailing positions. The following two
lines are equivalent:
zip_by { f(@_) } [ 1, 2, 3 ], [ "a", "b" ]
f( 1, "a" ), f( 2, "b" ), f( 3, undef )
The item function is called by "map", so if it returns a list, the
entire list is included in the result. This can be useful for example,
for generating a hash from two separate lists of keys and values
my %nums = zip_by { @_ } [qw( one two three )], [ 1, 2, 3 ];
# %nums = ( one => 1, two => 2, three => 3 )
(A function having this behaviour is sometimes called "zipWith", e.g.
in Haskell, but that name would not fit the naming scheme used by this
module).
unzip_by
$arr0, $arr1, $arr2, ... = unzip_by { ITEMFUNC } @vals
Since version 0.09.
Returns a list of ARRAY references containing the values returned by
the function block, when invoked for each of the values given in the
input list. Each of the returned ARRAY references will contain the
values returned at that corresponding position by the function block.
That is, the first returned ARRAY reference will contain all the values
returned in the first position by the function block, the second will
contain all the values from the second position, and so on.
my ( $firstnames, $lastnames ) = unzip_by { m/^(.*?) (.*)$/ } @names;
If the function returns lists of differing lengths, the result will be
padded with "undef" in the missing elements.
This function is an inverse of "zip_by", if given a corresponding
inverse function.
extract_by
@vals = extract_by { SELECTFUNC } @arr
Since version 0.05.
Removes elements from the referenced array on which the selection
function returns true, and returns a list containing those elements.
This function is similar to "grep", except that it modifies the
referenced array to remove the selected values from it, leaving only
the unselected ones.
my @red_balls = extract_by { $_->color eq "red" } @balls;
# Now there are no red balls in the @balls array
This function modifies a real array, unlike most of the other functions
in this module. Because of this, it requires a real array, not just a
list.
This function is implemented by invoking "splice" on the array, not by
constructing a new list and assigning it. One result of this is that
weak references will not be disturbed.
extract_by { !defined $_ } @refs;
will leave weak references weakened in the @refs array, whereas
@refs = grep { defined $_ } @refs;
will strengthen them all again.
extract_first_by
$val = extract_first_by { SELECTFUNC } @arr
Since version 0.10.
A hybrid between "extract_by" and "List::Util::first". Removes the
first element from the referenced array on which the selection function
returns true, returning it.
As with "extract_by", this function requires a real array and not just
a list, and is also implemented using "splice" so that weak references
are not disturbed.
If this function fails to find a matching element, it will return an
empty list in list context. This allows a caller to distinguish the
case between no matching element, and the first matching element being
"undef".
weighted_shuffle_by
@vals = weighted_shuffle_by { WEIGHTFUNC } @vals
Since version 0.07.
Returns the list of values shuffled into a random order. The
randomisation is not uniform, but weighted by the value returned by the
"WEIGHTFUNC". The probabilty of each item being returned first will be
distributed with the distribution of the weights, and so on recursively
for the remaining items.
bundle_by
@vals = bundle_by { BLOCKFUNC } $number, @vals
Since version 0.07.
Similar to a regular "map" functional, returns a list of the values
returned by "BLOCKFUNC". Values from the input list are given to the
block function in bundles of $number.
If given a list of values whose length does not evenly divide by
$number, the final call will be passed fewer elements than the others.
EXPORTS
This module exports nothing by default. You can import functions by
name, or get everything with the ":all" tag.
SEE ALSO
List::Util, List::SomeUtils and List::UtilsBy, obviously.
Also see "Util::Any", which unifies many more util modules, and also
lets you rename functions as part of the import.
BUGS
Please report any bugs or feature requests to
"bug-list-allutils@rt.cpan.org", or through the web interface at
<http://rt.cpan.org>. I will be notified, and then you'll
automatically be notified of progress on your bug as I make changes.
Bugs may be submitted at
<https://github.com/houseabsolute/List-AllUtils/issues>.
I am also usually active on IRC as 'autarch' on "irc://irc.perl.org".
SOURCE
The source code repository for List-AllUtils can be found at
<https://github.com/houseabsolute/List-AllUtils>.
DONATIONS
If you'd like to thank me for the work I've done on this module, please
consider making a "donation" to me via PayPal. I spend a lot of free
time creating free software, and would appreciate any support you'd
care to offer.
Please note that I am not suggesting that you must do this in order for
me to continue working on this particular software. I will continue to
do so, inasmuch as I have in the past, for as long as it interests me.
Similarly, a donation made in this way will probably not make me work
on this software much more, unless I get so many donations that I can
consider working on free software full time (let's all have a chuckle
at that together).
To donate, log into PayPal and send money to autarch@urth.org, or use
the button at <https://www.urth.org/fs-donation.html>.
AUTHOR
Dave Rolsky <autarch@urth.org>
CONTRIBUTORS
• Andy Jack <github@veracity.ca>
• Dave Jacoby <jacoby.david@gmail.com>
• Karen Etheridge <ether@cpan.org>
• Olaf Alders <olaf@wundersolutions.com>
• Ricardo Signes <rjbs@cpan.org>
• Yanick Champoux <yanick@babyl.dyndns.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2021 by Dave Rolsky.
This is free software, licensed under:
The Artistic License 2.0 (GPL Compatible)
The full text of the license can be found in the LICENSE file included
with this distribution.
perl v5.32.1 2021-09-22 List::AllUtils(3pm)
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