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Re: permutations of array

by jynx (Priest)
on Feb 22, 2002 at 05:28 UTC ( #146883=note: print w/replies, xml ) Need Help??

in reply to permutations of array

a couple of things,

The major problem with the code you have there is that it doesn't give combinations of separated list items, it only gives items from one point forward. As an example:
for n=3, with items 1,2, and 3, i get the following from your code:
1 2
1 2 3
2 3
Note the missing '1 3' case. For the items 1,2,3, and 4, '134', '124', '13', '14', etc would be missing.

Merlyn's snippets are a nice and easy way to go; a simple transformation and they will return an array of strings instead of an AoA. As an exercise, i chalked up a non-recursive solution as well; it returns an array of arrays as merlyn's does.

sub combinations { my (@comb, $pos); my $limit = 2**@_; while (my $item = shift) { my $step = 2**@_; for ($pos = 0; $pos < $limit; $pos += $step) { push @{$comb[$pos++]}, $item for 1..$step; } } return @comb, []; }

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[ovedpo15]: consider the following format of strings: some_data-doesn't- matter,value. how I get the value with regex? it should be after the last comma (last string)
[Corion]: Text::CSV_XS for all your CSV file parsing needs. Other than that, what problems do you have with perlre, and capturing everything after the comma? Also, index and substr would also work.
[choroba]: my ($value) = $string =~ /.*,(.*)/

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