in reply to Finding a random position within a long string (Activeperl Build 822)

Depending on what you mean by "somehow equally distributed over the string", this may do the trick 
my $percent = 10;
my $string = 'A' x 20;

for ( 1 .. $percent / 100 * length $string ) {
    my $pos = int rand length $string;
    substr( $string, $pos, 1 ) = '?';
}

[download]

Update: int isn't needed

Replies are listed 'Best First'.
Re^2: Finding a random position within a long string (Activeperl Build 822)
by mwah (Hermit) on Oct 12, 2007 at 21:47 UTC
    FunkyMonk: this may do the trick

    try: 
    my $percent = 10;
my $string = 'A' x 1_000_000;

for ( 1 .. $percent / 100 * length $string ) {
    my $pos = int rand length $string;
    substr( $string, $pos, 1 ) = '?';
}
print $string =~ y/?//;

    [download]
    Sth. like this is the approach I initially took (and failed).

    If you check that out (with a larger string), youll see the print-
    out from the last line will approach 0xffff.

    That means (I'm struggling to say this) 
       In Activeperl/Win, the RAND_MAX of 
   the underlying clib is promoted 
   into perl?
    Is this documented?

    Regards & Thanks

    mwa
[reply]
[d/l]
Re^2: Finding a random position within a long string (Activeperl Build 822)
by kyle (Abbot) on Oct 12, 2007 at 21:39 UTC

    This might get a little fewer than the percentage requested because it's possible for it to pick the same position more than once. Try setting $percent = 90 for a good demonstration. I ran it ten times, and it never replaced more than 13/20 (well short of the expected 18/20).

[reply]
[d/l]
      I took "about ~10%" to mean about 10% ;)

[reply]
[d/l]
[select]

In Section Seekers of Perl Wisdom