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Subject Author Date
checking for duplicates in a string John 02-23-2008
Posted by John on February 23, 2008, 6:18 am
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 Hi

Consider a string $packed consisting of "AAXYGHDRJKYYXYZZGH"
This represent items of two chars eg AA XY GH etc.
I need to remove duplicates.
I can do it by 'unpacking' and repacking using two loops such as

for (my $j=0; $j<$total; $j=$j+2) {
my $part1=substr($packed,$j,2);
etc etc.

But is there a better, dare I say, elegant, way?

Regards
John



Posted by Gunnar Hjalmarsson on February 23, 2008, 6:36 am
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 John wrote:
> Consider a string $packed consisting of "AAXYGHDRJKYYXYZZGH"
> This represent items of two chars eg AA XY GH etc.
> I need to remove duplicates.
> I can do it by 'unpacking' and repacking using two loops such as
>
> for (my $j=0; $j<$total; $j=$j+2) {
> my $part1=substr($packed,$j,2);
> etc etc.
>
> But is there a better, dare I say, elegant, way?

my $packed = 'AAXYGHDRJKYYXYZZGH';
my %seen;
print join(' ', map $seen++ ? () : $_, $packed =~ /../g), "\n";

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Posted by Gunnar Hjalmarsson on February 23, 2008, 7:39 am
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Gunnar Hjalmarsson wrote:
>
> my $packed = 'AAXYGHDRJKYYXYZZGH';
> my %seen;
> print join(' ', map $seen++ ? () : $_, $packed =~ /../g), "\n";

The grep() function is more to the point:

print join(' ', grep !$seen++, $packed =~ /../g), "\n";

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Posted by Ben Morrow on February 23, 2008, 7:07 pm
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> John wrote:
> > Consider a string $packed consisting of "AAXYGHDRJKYYXYZZGH"
> > This represent items of two chars eg AA XY GH etc.
> > I need to remove duplicates.
> > I can do it by 'unpacking' and repacking using two loops such as
> >
> > for (my $j=0; $j<$total; $j=$j+2) {
> > my $part1=substr($packed,$j,2);

Hmm... even if you *did* want to unpack, this is a bad way to do it.
Gunnar's /../g is much better, and unpack '(A2)*' better again.

> > etc etc.
> >
> > But is there a better, dare I say, elegant, way?
>
> my $packed = 'AAXYGHDRJKYYXYZZGH';
> my %seen;
> print join(' ', map $seen++ ? () : $_, $packed =~ /../g), "\n";

That still unpacks and repacks.

s/(..)/$seen++ ? '' : $1/ge;

Ben


Posted by John on February 24, 2008, 6:31 am
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>
>> John wrote:
>> > Consider a string $packed consisting of "AAXYGHDRJKYYXYZZGH"
>> > This represent items of two chars eg AA XY GH etc.
>> > I need to remove duplicates.
>> > I can do it by 'unpacking' and repacking using two loops such as
>> >
>> > for (my $j=0; $j<$total; $j=$j+2) {
>> > my $part1=substr($packed,$j,2);
>
> Hmm... even if you *did* want to unpack, this is a bad way to do it.
> Gunnar's /../g is much better, and unpack '(A2)*' better again.
>
>> > etc etc.
>> >
>> > But is there a better, dare I say, elegant, way?
>>
>> my $packed = 'AAXYGHDRJKYYXYZZGH';
>> my %seen;
>> print join(' ', map $seen++ ? () : $_, $packed =~ /../g), "\n";
>
> That still unpacks and repacks.
>
> s/(..)/$seen++ ? '' : $1/ge;
>
> Ben
>

Many thanks. It is taken me most of the morning to work out why it works,
but it does.
Thanks again
John




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