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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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