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Re: Extracting Unique Characters from a Array

by mreece (Friar)
on Sep 07, 2006 at 17:41 UTC ( #571757=note: print w/replies, xml ) Need Help??


in reply to Extracting Unique Characters from a Array

array elements are not unique, but hash keys are, so a common approach is to use the uniqueness of hash keys to resolve your array.

if you want to preserve the original order, you can do this:

my @nums = qw(2 1 3 5 4 5 4 3 2 1); # order is not important my @unique; # new list of unique elements my %seen; # numbers i have seen so far foreach my $x ( @nums ) { # check each number if ( ! $seen{$x} ) { # skip if we already saw this one $seen{$x} = 1; # note we have seen this one now push @unique, $x; # and store to new list } } ## TODO: do something with @unique
if you want to sort the resulting list, you can do this:
my @nums = qw(2 1 3 5 4 5 4 3 2 1); # order is not important my %seen = map { $_ => 1 } @nums; # build a hash; keys will be unique! @nums = sort keys %seen; # replace old list with new sorted list ## TODO: do something with @nums
another approach, as rsriram demonstrated above, is to sort first, then loop and look for repeating values:
my @nums = qw(2 1 3 5 4 5 4 3 2 1); @nums = sort @nums; my @unique; my $previous; foreach my $current ( @nums ) { # check each number next if $current eq $previous; # duplicate! push @unique, $current; # store to new list $previous = $current; # 'current' becomes 'previous' } ## TODO: do something with @unique
(updated to fix some silly issues with untested code)

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