Okay, here is some code to demonstrate the test that tilly described. I'm posting this because it gave me a couple of more chances to abuse the language.
#!/usr/bin/perl -w
use strict;
exit main();
# This is not tilly's recommended test for how random an
# ordering is. Repeatedly give a sorted list of numbers
# (if not using numbers, swap the < line for the "lt"
# line) to your randomizer and pass the results to
# cntincseq(). If your randomizer is good, then
# cntincseq() will return values that are distributed
# around something close to ( list size / 2 ).
sub cntincseq (\@) {
my( $aList )= @_;
my %seq;
@seq{ 0..$#{$aList} }= @$aList;
my( $idx, $cnt )= 0..1;
while( ++$idx < @$aList ) {
$cnt++ if $seq{$idx} < $seq{$idx-1}
# $cnt++ if $seq{$idx} lt $seq{$idx-1}
}
return $cnt;
}
sub validate ($&$) {
my( $cnt, $munge, $size )= @_;
my @counts;
for( 1..$cnt ) {
my @list= 1..$size;
&$munge( \@list );
push @counts, cntincseq( @list );
print " ",$counts[-1];
}
return @counts;
}
sub fy {
my( $aList )= @_;
for( reverse 2..@$aList ) {
my $i= rand($_);
@$aList[$_-1,$i]= @$aList[$i,$_-1];
}
}
sub hash {
my %hash;
for( @{$_[0]} ) {
$hash{rand()}= $_;
}
@{$_[0]}= values %hash;
}
sub main {
$|= 1;
my $tot;
my @counts= validate( 10, \&fy, 10000 );
# And here we have a particularly nasty abuse
# of C<map> for entertainment purposes only.
# Do not use in production code!
print "\nFisher-Yates: ",
($tot=0,map{$tot+=$_}@counts)[-1]/@counts, "\n";
@counts= validate( 10, \&hash, 10000 );
print "\nTye hash: ",
($tot=0,map{$tot+=$_}@counts)[-1]/@counts, "\n";
return 0;
}
Here are the results of comparing Fisher-Yates to my hash randomizer:
4987 4974 5022 5012 5078 4967 4996 5007 4998 4990
Fisher-Yates: 5003.1
4368 4542 4558 4529 4586 4601 4581 4566 4549 4535
Tye hash: 4541.5
Grumble... Back to that work on my bucketless hash table...
Update: Having just barely posted this, I think perhaps my test is similar but not quite the same as the test tilly described. I started writing the described test then mistakenly thought I could make it work on a wider selection of inputs, fixed what looked like a typo, and got a reasonable but different test out of it.
Update 2: And it isn't nearly as good of a test. I'll follow-up with some discussion in another node in a bit.
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tye
(but my friends call me "Tye")
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