http://www.perlmonks.org?node_id=1001046


in reply to Send x% of the users to A, the rest to B

This one-liner shows that if you use rand() < 0.5 to decide between locations -- even if the rand calls are in different invocations of perl -- the distribution will be fairly split: 

perl -E"{++$t;$r=`perl -E\"say rand()\"`;$r<.5?++$a:++$b; printf qq[\r
+%.3f : %.3f], $a*100/$t, $b*100/$t; redo}"
49.350 : 50.650

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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.

RIP Neil Armstrong

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Re^2: Send x% of the users to A, the rest to B
by Perleone (Initiate) on Oct 27, 2012 at 20:04 UTC
    Cool snippet! Interesting to see that (at least on my Debian box) it takes a few dozen iterations to actually reach middle ground: 
    perl -Mstrict -Mwarnings -E 'my $WIDTH = 50;
my ( $try, $i, $j ) = (0) x 3;
for ( 1 .. 40 ) {
    ++$try;
    my $rand = `perl -E "say rand()"`;
    $rand < .5 ? ++$i : ++$j;
    printf qq[%${WIDTH}s : %s\n],
      "#" x ( $i * $WIDTH / $try ),
      "#" x ( $j * $WIDTH / $try );
}'

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[d/l]
      Interesting to see that ... it takes a few dozen iterations to actually reach middle ground:

      That is the nature of randomness. If it was exactly 50:50, it wouldn't be random.

      But the more trials you run, the closer it will tend. This is more evident if you run this version with various different resets:

      C:\test>perl 
-E"{++$t;$r=`perl -E\"say rand()\"`;$r<.5?++$a:++$b; printf qq[\r%.3f 
+: %.3f], $a*100/$t, $b*100/$t; $t>$ARGV[0] and say and $t=$a=$b=0; re
+do}" 10
45.455 : 54.545
27.273 : 72.727
36.364 : 63.636
54.545 : 45.455
72.727 : 27.273
63.636 : 36.364
36.364 : 63.636
45.455 : 54.545
27.273 : 72.727
36.364 : 63.636
72.727 : 27.273
45.455 : 54.545
54.545 : 45.455
63.636 : 36.364

C:\test>perl 
-E"{++$t;$r=`perl -E\"say rand()\"`;$r<.5?++$a:++$b; printf qq[\r%.3f 
+: %.3f], $a*100/$t, $b*100/$t; $t>$ARGV[0] and say and $t=$a=$b=0; re
+do}" 100
52.475 : 47.525
52.475 : 47.525
52.475 : 47.525
46.535 : 53.465
45.545 : 54.455
51.485 : 48.515
41.584 : 58.416
46.535 : 53.465
42.574 : 57.426
40.594 : 59.406

C:\test>perl 
-E"{++$t;$r=`perl -E\"say rand()\"`;$r<.5?++$a:++$b; printf qq[\r%.3f 
+: %.3f], $a*100/$t, $b*100/$t; $t>$ARGV[0] and say and $t=$a=$b=0; re
+do}" 1000
49.750 : 50.250
51.349 : 48.651
48.651 : 51.349
53.047 : 46.953

      [download]
      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.

      RIP Neil Armstrong
[reply]
[d/l]

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