in reply to RE: Randomize List of items
in thread Randomize List of items
I'm not sure how your algorithm is different then mine. You start from the back, I start from the front, but if you compare the two side-by-side, they are almost identical.
My Original post - Non-Biased version | Alokito's version | Fisher-Yates Shuffle |
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my @lList = (1..10); | my @a = (1 .. 10); | my $array = shift; |
my ($lPos, $lRand); | print join("\t", @a),"\n"; | my $i; |
# For every position in the list, swap it with a random # position earlier in the list. |
#starting from the end and working back | |
foreach $lPos (1..$#list) { | for ($i = $#a; $i > 0; $i--) { | for ($i = @$array; --$i; ) { |
# pick a random guy to stuff in the ith slot | ||
$lRand = int(rand($lPos+1)); | $guy = int(rand($i + 1)); | my $j = int rand ($i+1); |
#snatch the guy out, and stuff him in! | next if $i == $j; | |
@lList$lPos, $lRand = @lList$lRand, $lPos; | splice(@a, $i, 0, splice(@a, $guy, 1)); | @$array$i,$j = @$array$j,$i; |
} | } | } |
print join("\t", @a),"\n"; |
When I posted this, I had not realized it was so similar to the one in the faq, the fisher_yates_shuffle. The only real difference is fisher-yates does not allow an element to stay in the same position. I don't think this is necessary. If someone knows why this is done, I would love to learn it.
Alokito,
You seem to imply that my solution either does not randomize in place, or is biased. To quote:
Bah, all the solutions I have seen either violate the order not to create new lists, or seem to produce biased results. I think I have found a way to do neither.But the truth is, our code does almost the same thing, just from different directions. Am I missing something?
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