Condition-based perl splitting array using grep

Question

I have Perl code that looks something like this:

my @array = map { rand } ( 1..100 ); my @matching = grep { $_ == $condition } @array; @array = grep { $_ != $condition } @array; 

This works fine, but what I would like to do is split the original array into two based on one operation ... I think I perform twice as many operations as necessary.

Help rate! Thank you

Answer 1

The easiest way is to iterate your array and pass the values ​​to either of the two arrays depending on the condition, as in the example below.

 for (@array) { if ($_ % 2) {push @odd, $_} else {push @even, $_} } 

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If you want to change the original array:

 for (my $i =0; $i < @array; ++$i) { if ($array[$i] % 2) { push @odd, splice (@array, $i--, 1); } } 

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Why didn’t you recommend List :: MoreUtils :: part?

This module may not exist on the target system, which is always annoying.

Also, on the system I ran tests, I found that List::MoreUtils::part was twice as slow as the first fragment in this post, although with different implementations of part this could be the other way around.

Answer 2

Here the part from List :: MoreUtils comes in handy.

 use List::MoreUtils qw'part'; my($even,$odd) = part { $_ % 2 } @array; 

This works great if you want each input element to be in the same output array.

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If you want to possibly put them in multiple arrays, you should loop them yourself.
The best way to do this is with a foreach loop.

 my(@div2,@div3); for my $elem (@array){ push @div2, $elem unless $elem % 2; push @div3, $elem unless $elem % 3; } 

If you need to do a lot of these tests, you might want to focus on what your testing is against.

 my %div; for my $elem (@array){ for my $div (2,3,5,7,11,13){ push @{ $out{$div} }, $elem unless $elem % $div; } } 

Answer 3

I like the simplicity of the List::MoreUtils ' part function:

 sub part (&@) { my ($code, @list) = @_; my @parts; push @{ $parts[ $code->($_) ] }, $_ foreach @list; return @parts; } 

The resulting @parts array is an arrayrefs array. @$parts[0] is an array of elements that return false. @$parts[1] returns true.