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Re: 'grouping' substrings?

by murugu (Curate)
on Feb 01, 2006 at 16:29 UTC ( [id://527101]=note: print w/replies, xml ) Need Help??


in reply to 'grouping' substrings?

I have come up with this. I dont know whether using $& is effecient or not. 

use strict;
use warnings;
my $seq="IIIIIMMMMMMMMMMMOOOOOOOOOOOOOOOOMMMMMMMMMMMMMIIIIIMMMMMMMMMOO
+OOO
+OOOOOOOOOMMMMMMMMMMMMMIIIMMMMMMMMMMMOOOOOOOOOOOOOOOMMMMMMMMMMMIIIIIIM
+MMMMMMMMMMMMOOOOOOOOOOOOOOOOOOOOOOOMMMMMMMIIIMMMMMMMMMOOOOOOOOOOOOOOO
+OOOOOOOOOOOOMMMMMMMIIIIMMMMMMMMMMMOOOOOOOOOOOOOOOOOOOOOMMMMMMMIIIMMMM
+MMMMMOOOOOOOOOOOOOOOOOOOOOOOOOMMMMMMMMMIIIMMMMMMMMMMMOOOOOOOOOOOOOOOO
+OMMMMMMMMI";
while ($seq=~/(M+)/g)  {
    my $l = pos($seq);
    print $l-length($&)+1," to ",$l,$/;
}

[download]

Regards,
Murugesan Kandasamy
use perl for(;;);

Replies are listed 'Best First'.
Re^2: 'grouping' substrings?
by revdiablo (Prior) on Feb 01, 2006 at 16:42 UTC
    I dont know whether using $& is effecient or not.

    Using $& is not efficient, and usually to be avoided. See the entry in perlvar for details.

    Update: perhaps I was a bit imprecise. I'd say something that "imposes a considerable performance penalty on all regular expression matches" is inefficient, but I guess it depends on what type of inefficiency we're talking about.

[reply]

      That's not exactly true. $& is only inefficient if you have another regexp in your program which doesn't capture.

      However, it's use is discouraged, since captures can perform the same task without the "effect at a distance" of $&.

      In this case, just replace $& with $1, and you're set.

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