List::AllUtils (3)
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NAME
List::AllUtils - Combines List::Util, List::SomeUtils and List::UtilsBy in one bite-sized packageVERSION
version 0.12SYNOPSIS
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. Similar, List::SomeUtils has some small overlap with List::UtilsBy. "List::AllUtils" always favors the version provided by List::Util, List::SomeUtils or List::UtilsBy in that order.The docs below come from List::Util 1.31, List::SomeUtils 0.50, and List::UtilsBy 0.10.
LIST-REDUCTION FUNCTIONS
The following set of functions all reduce a list down to a single value.reduce BLOCK LIST
Reduces Returns the result of the last call to
$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
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 remaining list-reduction functions are all specialisations of this generic idea.
first BLOCK LIST
Similar to "grep" in that it evaluates
$foo = first { defined($_) } @list # first defined value in @list
$foo = first { $_ > $value } @list # first value in @list which
# is greater than $value
This function could be implemented using "reduce" like this
$foo = reduce { defined($a) ? $a : wanted($b) ? $b : undef } undef, @list
for example wanted() could be defined() which would return the first defined value in @list
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
This function could be implemented using "reduce" like this
$foo = reduce { $a > $b ? $a : $b } 1..10
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
This function could be implemented using "reduce" like this
$foo = reduce { $a gt $b ? $a : $b } 'A'..'Z'
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
This function could be implemented using "reduce" like this
$foo = reduce { $a < $b ? $a : $b } 1..10
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
This function could be implemented using "reduce" like this
$foo = reduce { $a lt $b ? $a : $b } 'A'..'Z'
sum LIST
Returns the sum of all the elements in
$foo = sum 1..10 # 55
$foo = sum 3,9,12 # 24
$foo = sum @bar, @baz # whatever
This function could be implemented using "reduce" like this
$foo = reduce { $a + $b } 1..10
sum0 LIST
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.pairgrep BLOCK KVLIST
Similar to perl's "grep" keyword, but interprets the given list as an
even-sized list of pairs. It invokes the Returns an even-sized list of those pairs for which the
@subset = pairgrep { $a =~ m/^[[:upper:]]+$/ } @kvlist
Similar to "grep", "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 BLOCK KVLIST
Similar to the "first" function, but interprets the given list as an
even-sized list of pairs. It invokes the Returns the first pair of values from the list for which the
( $key, $value ) = pairfirst { $a =~ m/^[[:upper:]]+$/ } @kvlist
Similar to "grep", "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 BLOCK KVLIST
Similar to perl's "map" keyword, but interprets the given list as an
even-sized list of pairs. It invokes the Returns the concatenation of all the values returned by the
@result = pairmap { "The key $a has value $b" } @kvlist
Similar to "map", "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.
pairs KVLIST
A convenient shortcut to operating on even-sized lists of pairs, this
function returns a list of
pairmap { [ $a, $b ] } KVLIST
It is most convenient to use in a "foreach" loop, for example:
foreach ( pairs @KVLIST ) {
my ( $key, $value ) = @$_;
...
}
pairkeys KVLIST
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
pairmap { $a } KVLIST
pairvalues KVLIST
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
pairmap { $b } KVLIST
OTHER FUNCTIONS
shuffle LIST
Returns the elements of
@cards = shuffle 0..51 # 0..51 in a random order
List::SomeUtils FUNCTIONS
Junctions
Treatment of an empty listThere 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
all_u
Returns a true value if all items in
print "All values are non-negative"
if all { $_ >= 0 } ($x, $y, $z);
For an empty
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
any_u
Returns a true value if any item in
print "At least one non-negative value"
if any { $_ >= 0 } ($x, $y, $z);
For an empty
Thus, "any_u(@list)" is equivalent to "@list ? any(@list) : undef".
none
none_u
Logically the negation of "any". Returns a true value if no item in
print "No non-negative values"
if none { $_ >= 0 } ($x, $y, $z);
For an empty
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
notall_u
Logically the negation of "all". Returns a true value if not all items in
print "Not all values are non-negative"
if notall { $_ >= 0 } ($x, $y, $z);
For an empty
Thus, "notall_u(@list)" is equivalent to "@list ? notall(@list) : undef".
one
one_u
Returns a true value if precisely one item in
print "Precisely one value defined"
if one { defined($_) } @list;
Returns false otherwise.
For an empty
The expression "one BLOCK LIST" is almost equivalent to "1 == true BLOCK LIST", except for short-cutting. Evaluation of
Transformation
applyApplies
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 }
insert_after
Inserts
my @list = qw/This is a list/;
insert_after { $_ eq "a" } "longer" => @list;
print "@list";
__END__
This is a longer list
insert_after_string
Inserts
my @list = qw/This is a list/; insert_after_string "a", "longer" => @list; print "@list"; __END__ This is a longer list
pairwise
Evaluates
@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
zip
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
distinct
Returns a new list by stripping duplicate values in
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 '', 'S1', A5' and complains about "Use of uninitialized value" my @s = distinct '', undef, 'S1', 'A5' # returns undef, 'S1', A5' and complains about "Use of uninitialized value" 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
my @x = singleton 1,1,2,2,3,4,5 # returns 3 4 5
Partitioning
afterReturns a list of the values of
@x = after { $_ % 5 == 0 } (1..9); # returns 6, 7, 8, 9
after_incl
Same as "after" but also includes the element for which
before
Returns a list of values of
before_incl
Same as "before" but also includes the element for which
part
Partitions
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 { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
Iteration
each_arrayCreates an array iterator to return the elements of the list of arrays
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
Like each_array, but the arguments are references to arrays, not the plain arrays.
natatime
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
bsearchPerforms a binary search on
Returns a boolean value in scalar context. In list context, it returns the element if it was found, otherwise the empty list.
bsearchidx
bsearch_index
Performs a binary search on
Returns the index of found element, otherwise "-1".
"bsearch_index" is an alias for "bsearchidx".
firstval
first_value
Returns the first element in
"first_value" is an alias for "firstval".
onlyval
only_value
Returns the only element in
"only_value" is an alias for "onlyval".
lastval
last_value
Returns the last value in
"last_value" is an alias for "lastval".
firstres
first_result
Returns the result of
"first_result" is an alias for "firstres".
onlyres
only_result
Returns the result of
"only_result" is an alias for "onlyres".
lastres
last_result
Returns the result of
"last_result" is an alias for "lastres".
indexes
Evaluates
@x = indexes { $_ % 2 == 0 } (1..10); # returns 1, 3, 5, 7, 9
firstidx
first_index
Returns the index of the first element in
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
only_index
Returns the index of the only element in
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
last_index
Returns the index of the last element in
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_byReturns the list of values sorted according to the string values returned by the
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; $_ } @strings
This sorts strings by generating sort keys which zero-pad the embedded numbers to some level (9 digits in this case), helping to ensure the lexical sort puts them in the correct order.
nsort_by
Similar to sort_by but compares its key values numerically.
Counting and calculation
trueCounts the number of elements in
printf "%i item(s) are defined", true { defined($_) } @list;
false
Counts the number of elements in
printf "%i item(s) are not defined", false { defined($_) } @list;
minmax
Calculates the minimum and maximum of
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,
*By functions
rev_sort_byrev_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"
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
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 { $_->colour } @balls;
Because the values returned by the key function are used as hash keys, they ought to either be strings, or at least well-behaved as strings (such as numbers, or object references which overload stringification in a suitable manner).
zip_by
@vals = zip_by { ITEMFUNC } \@arr0, \@arr1, \@arr2,...
Returns a list of each of the values returned by the function block, when invoked with values from across each each of the given
my @transposition = zip_by { [ @_ ] } @matrix;
my @names = zip_by { "$_[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
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 probability 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.
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"
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
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 { $_->colour } @balls;
Because the values returned by the key function are used as hash keys, they ought to either be strings, or at least well-behaved as strings (such as numbers, or object references which overload stringification in a suitable manner).
zip_by
@vals = zip_by { ITEMFUNC } \@arr0, \@arr1, \@arr2,...
Returns a list of each of the values returned by the function block, when invoked with values from across each each of the given
my @transposition = zip_by { [ @_ ] } @matrix;
my @names = zip_by { "$_[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
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 probability 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 <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 through the
I am also usually active on
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 <www.urth.org/~autarch/fs-donation.html>.
AUTHOR
Dave Rolsky <autarch@urth.org>CONTRIBUTORS
- *
- Ricardo Signes <rjbs@cpan.org>
- *
- Yanick Champoux <yanick@babyl.dyndns.org>
COPYRIGHT AND LICENSE
This software is Copyright (c) 2016 by Dave Rolsky.This is free software, licensed under:
The Artistic License 2.0 (GPL Compatible)