in reply to Re^4: Out of Memory
in thread Out of Memory

Are you sure this is the most efficient way to do this?

Yes, I am quite sure.

  1. tr doesn't make copies, it operates in-place.
  2. It is optimised internally to recognise that when the source and replacements are identical, it is in 'counting mode' only.

For multi-character substring counting avoid creating the huge list:

$s = 'ab'x 10e6;;

++$n while $s=~ m[ab]g;;
print $n;;
10000000

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With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

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Re^6: Out of Memory
by Michael Kittrell (Novice) on Mar 28, 2013 at 19:31 UTC
    Ah that makes sense, I was wondering if it would not replace if both were the same.

    how does

    ++$n while $s=~ m[ab]g;;

    differ in execution from

    while($_=~s\0g) {count++}

    Thanks for sharing

[reply]
[d/l]
[select]
      how does ... differ in execution from ...

      Hm. "in execution"?

      1. The result -- the count -- is the same.
      2. The runtime is less than half:
        $s = 'ab'x 10e6;;

cmpthese -1, {
    a => q[ 
        my $n = 0; 
        while( $s =~ m[ab]g ){
            $n++
        };
    ],
    b=>q[
        my $n = 0; 
        ++$n while $s =~ m[ab]g;
    ],
};;

  s/iter    a    b
a   2.31   -- -37%
b   1.45  59%   --

        [download]
      3. It is easier to read.

      Don't use post increment if you aren't using the pre-increment value. Don't create scopes you don't need.

      Or, get into the habit of not doing anything you don't need to.

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority".
      In the absence of evidence, opinion is indistinguishable from prejudice.
[reply]
[d/l]
        Thank you for the very thorough explanation and proof.

        If you don't know where you're going, it doesn't matter when you get there.
[reply]

In Section Seekers of Perl Wisdom