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Answer: How do I shuffle an array?

by vroom (Pope)
on Jan 09, 2000 at 10:02 UTC ( #1905=categorized answer: print w/replies, xml ) Need Help??

Q&A > arrays > How do I shuffle an array? - Answer contributed by vroom

The Fisher-Yates shuffle is easy to code up:
# randomly permutate @array in place sub fisher_yates_shuffle { my $array = shift; my $i = @$array; while ( --$i ) { my $j = int rand( $i+1 ); @$array[$i,$j] = @$array[$j,$i]; } } fisher_yates_shuffle( \@array ); # permutes @array in place

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Re: Answer: How do I shuffle an array?
by runrig (Abbot) on Aug 21, 2002 at 16:40 UTC
    And mentioned numerous times in numerous places, the 'next if $i == $j' is unnecessary, as it rarely saves an element swap (except on the smallest of arrays), so it actually costs more to do the comparison every time rather than just swapping unconditionally.

    BTW, in case anyone was wondering who these guys Fisher and Yates were, here's some links. They're hard to find when almost every reference to Fisher and Yates (and especially with the term 'shuffle') on Google is a perl reference :-)

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