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Duplicates

Posted on 1998-09-29
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Last Modified: 2010-03-05
What is the most efficient way to strip duplicates from an array?
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Question by:IsleOfView
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b2pi earned 160 total points
ID: 1205023
perldoc perlfaq4

     a) If @in is sorted, and you want @out to be sorted:
 
             $prev = 'nonesuch';
             @out = grep($_ ne $prev && ($prev = $_), @in);
 
         This is nice in that it doesn't use much extra memory,
         simulating uniq(1)'s behavior of removing only adjacent
         duplicates.
 
     b) If you don't know whether @in is sorted:
 
             undef %saw;
             @out = grep(!$saw{$_}++, @in);
 
     c) Like (b), but @in contains only small integers:
 
             @out = grep(!$saw[$_]++, @in);
 
     d) A way to do (b) without any loops or greps:
 
             undef %saw;
             @saw{@in} = ();
             @out = sort keys %saw;  # remove sort if undesired
 

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