perlquestion
Anonymous Monk
<p>Howdy all,</p>
<p>I have a function that I use sometimes when I need permutations (I do permutation-testing often for stats problems). Currently I require the user to pass the "cardinality": how many different elements to put in each class. Let me give a simple example first, before I show the code:</p>
<code>
Data: a1, b2, c3
Cardinality: 1
Permutations:
{a1, b2},
{a1, c3},
{b2, c3},
Data: a1, b2, c3, d4
Cardinality: 2
Permutations:
{{a1, b2}, {c3, d4}}
{{a1, c3}, {b2, d4}}
{{a1, d4}, {c3, d4}}
</code>
<p>I hope that's reasonably clear: cardinality defines the size of the group I wish to obtain permutations of. The first example above was: all possible pairs of groups of one element. The second example was: all possible pairs of groups of three elements (triplets). Within a single permutation, no element can be repeated, and I take only unique permutations.</p>
<p>I am generating all these permutations into a data-structure for later use (e.g. passing them to other software, writing them to file with their results, sending them to a DB, etc.). The code that does this is pretty simple, but unfortunately it has required me to HARDCODE the cardinality. It looks like this:</p>
<code>
my @data;
if ($cardinality == 1) {
for (my $i = 0; $i < scalar(@$permlist); $i++) {
for (my $j = 0; $j < scalar(@$permlist); $j++) {
push @data, {
first => [$$permlist[$i]],
second => [$$permlist[$j]],
};
}
}
}
if ($cardinality == 2) {
for (my $i = 0; $i < scalar(@$permlist); $i++) {
for (my $j = 0; $j < scalar(@$permlist); $j++) {
for (my $k = 0; $k < scalar(@$permlist); $k++) {
for (my $p = 0; $p < scalar(@$permlist); $p++) {
push @data, {
first => [$$permlist[$i], $$permlist[$j]],
second => [$$permlist[$k], $$permlist[$p]],
};
}
}
}
}
}
</code>
<p>And so on for higher cardinality. I would prefer to have a generalized way of doing this, rather than needing a separate set of for-loops for each cardinality. Is that possible? I'm turned it over in my head, and haven't found a way yet.</p>
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