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Re: removing duplicate entries from an array

by BUU (Prior)
on Nov 07, 2005 at 20:47 UTC ( #506521=note: print w/replies, xml ) Need Help??


in reply to removing duplicate entries from an array

If you pull out your handy dandy perldoc and type 'perldoc -q duplicate', which searches for the word 'duplicate' in the FAQ section of the perldoc, you come upon this handy entry:
ded430-deb-175-30:/home/buu/torrent# perldoc -q duplicat Found in /usr/share/perl/5.8/pod/perlfaq4.pod How can I remove duplicate elements from a list or array? There are several possible ways, depending on whether the array + is ordered and whether you wish to preserve the ordering. a) If @in is sorted, and you want @out to be sorted: (this ass +umes all true values in the array) $prev = "not equal to $in[0]"; @out = grep($_ ne $prev && ($prev = $_, 1), @in); This is nice in that it doesn't use much extra memory, simu +lating uniq(1)'s behavior of removing only adjacent duplicates. The ", 1" guarantees that the express +ion is true (so that grep picks it up) even if the $_ is 0, "", or undef. b) If you don't know whether @in is sorted: undef %saw; @out = grep(!$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 e) Like (d), but @in contains only small positive integers: undef @ary; @ary[@in] = @in; @out = grep {defined} @ary; But perhaps you should have been using a hash all along, eh?

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