Splitting on change

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")
[download]

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?

thor

The only easy day was yesterday

Comment on Splitting on change Select or Download Code

Replies are listed 'Best First'.
Re: Splitting on change by Roy Johnson (Monsignor) on Dec 08, 2005 at 16:19 UTC
Elegant way to split into sequences of identical chars? includes several options. The one I like best is pKai's refinement. Caution: Contents may have been coded under pressure.	[reply]
Re: Splitting on change by ikegami (Patriarch) on Dec 08, 2005 at 16:25 UTC
`my $t = 0; my @x = grep $t^=1, split /(?<=(.))(?!\1)/, $x;` [download] `my @x; push(@x, $1) while $x =~ /((.)\2)/g;` [download] `my $t = 0; my @x = grep $t^=1, $x =~ /((.)\2)/g;` [download] `my $t = 0; my @x = grep $t^=1, map /((.)\2*)/g, $x;` [download] `$t` is for "toggle". `grep` is used to filter out every second item.	[reply] [d/l] [select]
Re: Splitting on change by Fletch (Bishop) 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";` [download] Update: Bleh, ignore me. Look at the other suggestions. Now where'd my caffeine go . . .	[reply] [d/l]


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