/ 
List-MoreUtils-0.400_005
River stage four • 815 direct dependents • 3342 total dependents
/ List::MoreUtils::Impl::Strict

NAME

List::MoreUtils::Impl::Strict - Provide strict List::MoreUtils implementation (originally by Tassilo von Parseval)

SYNOPSIS

use List::MoreUtils qw(:strict);

FUNCTIONS

any 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 value undefined"
  if any { ! defined($_) } @list;

Returns false otherwise, or undef if LIST is empty.

all BLOCK LIST

Returns a true value if all items in LIST meet the criterion given through BLOCK, or if LIST is empty. 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.

none BLOCK LIST

Logically the negation of any. Returns a true value if no item in LIST meets the criterion given through BLOCK, or if LIST is empty. 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.

notall 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 defined"
  if notall { defined($_) } @list;

Returns false otherwise, or undef if LIST is empty.

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;

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.

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.

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

apply BLOCK 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 }

before BLOCK LIST

Returns a list of values of LIST upto (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.

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.

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

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_val is an alias for firstval.

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_val is an alias for lastval.

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

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

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. 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

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.

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 { $idx[$++ % 3] } 1 .. 8; # [1, 4, 7], [2, 3, 5, 6, 8]

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.

SEE ALSO

List::Util

AUTHOR

Jens Rehsack <rehsack AT cpan.org>

Adam Kennedy <adamk@cpan.org>

Tassilo von Parseval <tassilo.von.parseval@rwth-aachen.de>

COPYRIGHT AND LICENSE

Some parts copyright 2011 Aaron Crane.

Copyright 2004 - 2010 by Tassilo von Parseval Copyright 2013 by Jens Rehsack

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.