in reply to Function over all letters in a string

TMWTOTDI, this one getting more milage out of each rand call: 
{
    my $r = substr rand, 2;
    sub crand() {
        length $r or $r = substr rand, 2;
        chop $r;
    }
}

s[(.)]{$1 x (1+crand/3)}ge;

[download]

Makeshifts last the longest.

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Re: Function over all letters in a string
by Abigail-II (Bishop) on Dec 01, 2003 at 10:35 UTC
    It looks cute, but it's wrong. About once every 10,000 times, rand() returns a number that's smaller than 0.0001, and that gets represented in scientific notation, meaning there are an 'e' and a '-' in the string. 
    #!/usr/bin/perl

use strict;
use warnings;

my $c = 0;

while (1) {
    $c ++;
    my $r = rand;
    die "Failed ($r) after $c attempts.\n" if substr ($r, 2) =~ /\D/;
}
 
__END__
Failed (1.13079331747201195e-05) after 17507 attempts.

    [download]

    Abigail

[reply]
[d/l]
      Thanks for the pointer. Simple fix: 
      {
    my $r = substr rand, 2;
    sub crand() {
        length $r or ($r = rand) =~ tr/0-9//cd;
        chop $r;
    }
}

s[(.)]{$1 x (1+crand/3)}ge;

      [download]
      On that note one could also 
      # ...
        length $r or ($r = rand) =~ tr/3-9//cd;
# ...

s[(.)]{$1 x crand/3}ge;

      [download]
      and even move the division up into crand although that's not a generic "cached rand" anymore.

      Makeshifts last the longest.

[reply]
[d/l]
[select]
        Well, if you initialize $r as substr rand, 2, you haven't solved the problem - $r can still contain non digits.
        On that note one could also 
        # ...
        length $r or ($r = rand) =~ tr/3-9//cd;
# ...

        [download]
        No, not really. What happens if rand returns a value whose stringification only contains 0, 1 and 2? $r will be empty.

        Besides, why are you caching the result of rand? Are you running out of random numbers? The overhead of a call to a user function (crand) is much higher than the overhead of a call to Perl primitive.

        Abigail

[reply]
[d/l]

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