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Splitting on change

by thor (Priest)
on Dec 08, 2005 at 16:15 UTC ( #515284=perlquestion: print w/replies, xml ) Need Help??

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

Greetings all,

The other day, I found myself in the position to split a string not on an explicit delimiter, but rather where the string changes. A quick example might be in order:

my $x = "AAAABBBCCCCCC"; my $regex = qr(); #this is my hang-up! my @x = split($regex, $x); #I want @x = ("AAAA", "BBB", "CCCCCC")
I've gotten close. For my regex, I have thus far qr((?:(\w))(?!\1)+). This produces an array of qw(AAA A BB B CCCCCC). The problem as I see it is the following passage from perldoc -f split:
If the PATTERN contains parentheses, additional list elements are created from each matching substring in the delimiter.
However, I don't see how I can get around using capturing parentheses given that I have to use a back reference in the regular expression. Does anyone have any experience with this problem?


The only easy day was yesterday

Replies are listed 'Best First'.
Re: Splitting on change
by Roy Johnson (Monsignor) on Dec 08, 2005 at 16:19 UTC
Re: Splitting on change
by ikegami (Pope) on Dec 08, 2005 at 16:25 UTC
    my $t = 0; my @x = grep $t^=1, split /(?<=(.))(?!\1)/, $x;
    my @x; push(@x, $1) while $x =~ /((.)\2*)/g;
    my $t = 0; my @x = grep $t^=1, $x =~ /((.)\2*)/g;
    my $t = 0; my @x = grep $t^=1, map /((.)\2*)/g, $x;

    $t is for "toggle". grep is used to filter out every second item.

Re: Splitting on change
by Fletch (Chancellor) on Dec 08, 2005 at 16:25 UTC

    Kludgy, but you could use what you've got and append every even element to the preceding odd element.

    my @result; while( my( $o, $e ) = splice( @tmp, 0, 2 ) ) { push @result, $o . $e } print join( "\n", @result ), "\n";

    Update: Bleh, ignore me. Look at the other suggestions. Now where'd my caffeine go . . .

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