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### Re: Finding unique elements in an array

by pelagic (Priest)
 on Mar 15, 2005 at 13:28 UTC ( #439619=note: print w/replies, xml ) Need Help??

in reply to Finding unique elements in an array

I don't remember where I pinched this one, it might have been around here somewhere ;-)
This shows some different ways to do it and benchmarks:
```use Benchmark;

my @list;
for ( 0..9999 )
{
push @list, sprintf "%d", 100 * rand ;
}

timethese(
1000,
{
'keys_map_1'        => sub { my @uniq = keys %{{ map {\$_ => 1}
+        @list }}; },
'keys_map_undef'    => sub { my @uniq = keys %{{ map {\$_ => un
+def}    @list }}; },
'grep_seen'         => sub { my %seen; my @uniq = grep ! \$seen
+{\$_}++, @list; },
}
);
__END__
Benchmark: timing 1000 iterations of grep_seen, keys_map_1, keys_map_u
+ndef...
grep_seen:     15 wallclock secs (14.86 usr +  0.01 sys = 14.87 CPU)
+@ 67.23/s (n=1000)
keys_map_1:     50 wallclock secs (46.78 usr +  0.83 sys = 47.61 CPU)
+@ 21.00/s (n=1000)
keys_map_undef: 43 wallclock secs (42.16 usr +  0.94 sys = 43.09 CPU)
+@ 23.21/s (n=1000)
The benchmark results are very much dependant of the size of the array. I took a 10,000 items array as an example.

Update:
To post something reasonable that does implement uniq as in OP's question, here's my solution (somewhat similar to Joost's):
```my @b = map {\$a[\$_] eq \$a[\$_ + 1] ? () : \$a[\$_]} 0..\$#a;

pelagic

Replies are listed 'Best First'.
Re^2: Finding unique elements in an array
by ikegami (Pope) on Mar 15, 2005 at 15:51 UTC
None of these perform the function of uniq as the parent requested. uniq only looks at the previous item, not all previous items.

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