Match 2 same characters

paragkalra has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Match 2 same characters by mr_mischief (Monsignor) on Mar 19, 2009 at 18:22 UTC
So what you want is a regular expression with a backreference. `my @array = qw( foo bar baz quux xyzzy); my @matched; for my $elem ( @array ) { push @matched, $elem if $elem =~ m/(.)\1/; } print "$_\n" for @matched;` [download] See perlre and search for "backreference" or for "find first doubled" for more explanation.	[reply] [d/l]
Re: Match 2 same characters by kennethk (Abbot) on Mar 19, 2009 at 18:09 UTC
Might I suggest that a C-style for loop combined with substr might be a more reasonable approach, especially since you want to match every character under the sun? Update: The literal solution could be obtained using `/(.)\1/` (see perlre).	[reply] [d/l]
Re: Match 2 same characters by bichonfrise74 (Vicar) on Mar 19, 2009 at 18:50 UTC
Hi, A simple array for-loop can do the trick... `#!/usr/bin/perl use strict; my @old_arrays = qw( aa aa bb bb cc dd ); my @new_arrays; push( @new_arrays, $old_arrays[0] ); for (my $i = 0; $i <= $#old_arrays; $i++) { push( @new_arrays, $old_arrays[$i] ) if ( ( $old_arrays[$i] ne $ol +d_arrays[$i-1] ) && $i > 0 ); } print "@new_arrays\n";` [download]	[reply] [d/l]
Re^2: Match 2 same characters by johngg (Canon) on Mar 19, 2009 at 23:59 UTC
A grep might be a bit simpler. I'm not sure why you push the first element outside of the loop and then have to test for element number inside. It seems to be an un-necessary complication. `use strict; use warnings; my @pets = qw{ gerbil parrot hamster cat poodle goldfish }; my @doubles = grep m{(.)\1}, @pets; print qq{$_\n} for @doubles;` [download] The output `parrot poodle` [download] I hope this is of interest. Cheers, JohnGG	[reply] [d/l] [select]
Re^3: Match 2 same characters by bichonfrise74 (Vicar) on Mar 20, 2009 at 01:46 UTC
Hi JohnGG, I totally misunderstood the question. Hehehe...	[reply]
Re: Match 2 same characters by paragkalra (Scribe) on Mar 19, 2009 at 18:59 UTC
Sorry for the typo. I was trying: if ( $_ =~ /(.){1}	[reply]
Re^2: Match 2 same characters by ikegami (Patriarch) on Mar 19, 2009 at 19:57 UTC
`{1}` is a quantifier. It modifies what the preceding atom (`(.)` in this case) matches. This and other quantifiers are documented in perlre.	[reply] [d/l] [select]
Re: Match 2 same characters by paragkalra (Scribe) on Mar 19, 2009 at 18:56 UTC
Thanks mr_mischief. It worked like a charm BTW I was trying: if ( $_ =~ /(.)\1/ ) What was wrong that	[reply]
Re: Match 2 same characters by paragkalra (Scribe) on Mar 19, 2009 at 18:19 UTC
Can't it be achieved through regular expressions?	[reply]