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FWIW. To the best of my ability to test it, and walking on the shoulders of those better versed in statistics than I, my implementation of Fisher-Yates algorithm compares favourably with that given in the FAQ.

Perhaps you would point out the flaws in my testing method?

Test code

#!/usr/bin/perl -w use strict; use vars qw/$size $iter/; use Benchmark qw(cmpthese); use Data::Dumper; $size ||= 1000; $iter ||= 1000; sub FAQ_FY { my $array = shift; my $i; for ($i = @$array; --$i; ) { my $j = int rand ($i+1); next if $i == $j; @$array[$i,$j] = @$array[$j,$i]; } } sub shuffl (\@) { my $r=pop; $a = $_ + rand @{$r} - $_ and @$r[$_, $a] = @$r[$a, $_] for (0..$#{$r}); } my @array = 1 .. $size; cmpthese(-1, { FAQ_FY => sub { FAQ_FY \@array }, shuffl => sub { shuffl @array }, }); my (%buckets, %d, @temp);; my @set = qw(A B C D); for (1 .. $iter ) { @temp=@set; FAQ_FY \@temp; $buckets{"@temp"}{FAQ_FY}++; @temp=@set; shuffl @temp; $buckets{"@temp"}{shuffl}++; } print "\npermutation | FAQ_FY | shuffl \n"; print "----------------------------------\n"; for my $key (sort keys %buckets) { printf "%8.8s: | %4d | %4d \n", $key, $buckets{$key}{FAQ_FY}, $buckets{$key}{shuffl}, $d{FAQ_FY}{Ex} += $buckets{$key}{FAQ_FY}; $d{FAQ_FY}{Ex2} += $buck +ets{$key}{FAQ_FY}**2; $d{shuffl}{Ex} += $buckets{$key}{shuffl}; $d{shuffl}{Ex2} += $buck +ets{$key}{shuffl}**2; } print "------------------------------------------------------\n"; printf "Std. Dev. | %0.3f | %0.3f \n", sqrt( ($d{FAQ_FY}{Ex2} - ($d{FAQ_FY}{Ex}**2/24))/23 ), sqrt( ($d{shuffl}{Ex2} - ($d{shuffl}{Ex}**2/24))/23 ); __END__

C:\test>199981 -size=100 -iter=100000 Benchmark: running FAQ_FY, shuffl, each for at least 1 CPU seconds... FAQ_FY: 2 wallclock secs ( 1.14 usr + 0.00 sys = 1.14 CPU) @ 39 +2.64/s (n=448) shuffl: 1 wallclock secs ( 1.08 usr + 0.00 sys = 1.08 CPU) @ 44 +2.70/s (n=479) Rate FAQ_FY shuffl FAQ_FY 393/s -- -11% shuffl 443/s 13% -- permutation | FAQ_FY | shuffl ---------------------------------- A B C D: | 4140 | 4221 A B D C: | 4231 | 4211 A C B D: | 4205 | 4151 A C D B: | 4247 | 4257 A D B C: | 4076 | 4275 A D C B: | 4107 | 4244 B A C D: | 4207 | 4165 B A D C: | 4159 | 4240 B C A D: | 3941 | 4187 B C D A: | 4136 | 4116 B D A C: | 4158 | 4126 B D C A: | 4185 | 4111 C A B D: | 4126 | 4231 C A D B: | 4224 | 4122 C B A D: | 4135 | 4139 C B D A: | 4123 | 4097 C D A B: | 4179 | 4001 C D B A: | 4228 | 4175 D A B C: | 4295 | 4057 D A C B: | 4264 | 4131 D B A C: | 4206 | 4169 D B C A: | 4138 | 4239 D C A B: | 4167 | 4208 D C B A: | 4123 | 4127 ------------------------------------------------------ Std. Dev. | 72.382 | 67.643 C:\test>

Nah! You're thinking of Simon Templar, originally played (on UKTV) by Roger Moore and later by Ian Ogilvy

In reply to Re: Re: Re: random elements from array - new twist by BrowserUk
in thread random elements from array - new twist by felwick

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