List::MoreUtils - Provide the stuff missing in List::Util
use List::MoreUtils qw(any all none notall true false firstidx first_index
lastidx last_index insert_after insert_after_string
apply after after_incl before before_incl indexes
firstval first_value lastval last_value each_array
each_arrayref pairwise natatime mesh zip uniq minmax);
List::MoreUtils provides some trivial but commonly needed functionality on lists
which is not going to go into List::Util.
All of the below functions are implementable in only a couple of lines of Perl code. Using the functions from this module however should give slightly better performance as everything is implemented in C. The pure-Perl implementation of these functions only serves as a fallback in case the C portions of this module couldn't be compiled on this machine.
Returns a true value if any item in LIST meets the criterion given through
BLOCK. Sets $_ for each item in LIST in turn:
print "At least one value undefined"
if any { !defined($_) } @list;
Returns false otherwise, or undef if LIST is empty.
Returns a true value if all items in LIST meet the criterion given through
BLOCK. Sets $_ for each item in LIST in turn:
print "All items defined"
if all { defined($_) } @list;
Returns false otherwise, or undef if LIST is empty.
Logically the negation of any. Returns a true value if no item in LIST meets the
criterion given through BLOCK. Sets $_ for each item in LIST in turn:
print "No value defined"
if none { defined($_) } @list;
Returns false otherwise, or undef if LIST is empty.
Logically the negation of all. Returns a true value if not all items in LIST meet
the criterion given through BLOCK. Sets $_ for each item in LIST in turn:
print "Not all values defined"
if notall { defined($_) } @list;
Returns false otherwise, or undef if LIST is empty.
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;
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;
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.
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.
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
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
Applies BLOCK to each item in LIST and returns a list of the values after BLOCK
has been applied. In scalar context, the last element is returned. 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 }
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 but also inclues the element for which BLOCK is true.
$_ for each element in LIST in turn.
before but also includes the element for which BLOCK is true.
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
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_val is an alias for firstval.
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_val is an alias for lastval.
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
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 retuns
the index of the last fetched set of values, as a scalar.
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
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.
Returns a new list by stripping duplicate values in LIST. 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
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.
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 { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]
Nothing by default. To import all of this module's symbols, do the conventional
use List::MoreUtils qw/:all/;
It may make more sense though to only import the stuff your program actually needs:
use List::MoreUtils qw/any firstidx/;
When LIST_MOREUTILS_PP is set, the module will always use the pure-Perl
implementation and not the XS one. This environment variable is really just
there for the test-suite to force testing the Perl implementation, and possibly
for reporting of bugs. I don't see any reason to use it in a production
environment.
This is version 0.22.
There is a problem with a bug in 5.6.x perls. It is a syntax error to write things like:
my @x = apply { s/foo/bar/ } qw/foo bar baz/;
It has to be written as either
my @x = apply { s/foo/bar/ } 'foo', 'bar', 'baz';
or
my @x = apply { s/foo/bar/ } my @dummy = qw/foo bar baz/;
Perl5.5.x and perl5.8.x don't suffer from this limitation.
If you have a functionality that you could imagine being in this module, please
drop me a line. This module's policy will be less strict than List::Util's when
it comes to additions as it isn't a core module.
When you report bugs, it would be nice if you could additionally give me the
output of your program with the environment variable LIST_MOREUTILS_PP set
to a true value. That way I know where to look for the problem (in XS,
pure-Perl or possibly both).
Credits go to a number of people: Steve Purkis for giving me namespace advice and James Keenan and Terrence Branno for their effort of keeping the CPAN tidier by making List::Utils obsolete.
Brian McCauley suggested the inclusion of apply() and provided the pure-Perl implementation for it.
Eric J. Roode asked me to add all functions from his module List::MoreUtil
into this one. With minor modifications, the pure-Perl implementations of those
are by him.
The bunch of people who almost immediately pointed out the many problems with the glitchy 0.07 release (Slaven Rezic, Ron Savage, CPAN testers).
A particularly nasty memory leak was spotted by Thomas A. Lowery.
Lars Thegler made me aware of problems with older Perl versions.
Anno Siegel de-orphaned each_arrayref().
David Filmer made me aware of a problem in each_arrayref that could ultimately lead to a segfault.
Ricardo Signes suggested the inclusion of part() and provided the Perl-implementation.
Robin Huston kindly fixed a bug in perl's MULTICALL API to make the XS-implementation of part() work.
A pile of requests from other people is still pending further processing in my mailbox. This includes:
Tassilo von Parseval, <tassilo.von.parseval@rwth-aachen.de>
Copyright (C) 2004-2006 by Tassilo von Parseval
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.4 or, at your option, any later version of Perl 5 you may have available.