|
Eyck has asked for the wisdom of the Perl Monks concerning the following question:
What's the best way to implement uniq for arrays?
What I've got is this:
#!/usr/bin/perl -w
@a=qw(ala ma kota tytus ma kolty a pies ma ale);
use Data::Dumper;
print Dumper(@a);
print "Sorted:\n";
print Dumper(sort @a);
print "Uniq:\n";
print Dumper(uniq(@a));
print "Uniq2:\n";
print Dumper(uniq(sort @a));
sub uniq {
my @out=();
my ($a,$lasta);
foreach $a (@_) {
push @out,$a unless (defined($lasta) && ($lasta eq $a)
+);
$lasta=$a;
};
return @out;
};
This works, but it seems a bit ugly, looks like it's copying stuff too much ( I would prefer to work on original array ) etc...
20050317 Edit by castaway: Changed title from 'uniq' |
Re: Finding Finding unique elements in an arrayue elements in an array
by holli (Abbot) on Mar 15, 2005 at 13:03 UTC
|
| [reply] |
Re: Finding unique elements in an array
by pelagic (Priest) on Mar 15, 2005 at 13:28 UTC
|
Please ignore:
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;
| [reply]
[d/l]
[select] |
|
|
None of these perform the function of uniq as the parent requested. uniq only looks at the previous item, not all previous items.
| [reply] |
Re: Finding unique elements in an array
by Joost (Canon) on Mar 15, 2005 at 13:08 UTC
|
Depending on what exactly you want to do with undefined values, this works.
#!/usr/bin/perl -w
@a=qw(ala ma kota tytus ma kolty a pies ma ale);
print join ", ", uniq( sort @a),"\n";
sub uniq {
my $last;
map { (defined($last) && $last eq $_) ? () : ($last = $_) } @_;
}
| [reply]
[d/l] |
Re: Finding unique elements in an array
by RazorbladeBidet (Friar) on Mar 15, 2005 at 13:14 UTC
|
I think that is probably the clearest way to do it. Here's a way (which I'm not 100% works 100% of the time) that operates on the original list... but as you can see, it's nowhere near as clear:
sub uniq2 {
my @out = ();
my ($a, $lasta);
for ( my $i = 0; $i < @_; $i++ ) {
splice @_, $i--, 1 if defined($lasta) && $_[$i] eq $lasta;
$lasta = $_[$i];
}
return @_;
}
I would stick with something similar to what you have above - it's easy to read, follow and maintain.
Although I'm sure someone else can think of an uber-elegant solution :)
--------------
It's sad that a family can be torn apart by such a such a simple thing as a pack of wild dogs
| [reply]
[d/l] |
Re: Finding unique elements in an array
by eyepopslikeamosquito (Archbishop) on Mar 15, 2005 at 13:04 UTC
|
It's in perlfaq4
"How can I remove duplicate elements from a list or array?".
Also, your line 19:
{push @out,$a;} unless (defined($lasta) && ($lasta eq $a));
gives me a syntax error.
| [reply]
[d/l] |
|
|
| [reply]
[d/l] |
|
|
| [reply]
[d/l] |
|
|
|
|
Re: Finding unique elements in an array
by Limbic~Region (Chancellor) on Mar 15, 2005 at 13:39 UTC
|
Eyck,
I will offer the same solution as I have to similar questions in the past. In my opinion, if you need to do things more than once in a program like sort a hash or get unique elements in an array, it is best to have a work-horse do the heavy lifting for you. While you haven't said this is the case here, it is always nice to have it in your back pocket.
| [reply]
[d/l] |
|
|
