Why don't people read FAQs any more?

How do I shuffle an array randomly?

Why don't people read FAQs any more?

Maybe because they don't know how? :)

perldoc -q random
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or one could take a look in the Perl FAQ here at PM, sneakily called Categorized Questions and Answers (array->how do I shuffle).

-- Hofmator

If you can ask here, you know how to search

You need to know this: The shuffle() routine implemented in List::Util is a fair shuffle; It is an implementation of the fisher-yates shuffle. Other recipies such as yours are not certain to be 'fair'. I don't know if yours is biased or not, but why leave it to chance when there's a perfectly good alternative built into a module that comes with Perl? I do know that it is very easy to get it wrong when writing an unbiased shuffle routine. Good thing someone included a fair, unbiased shuffle in List::Util

The OP's shuffle does have a bug. It should have rand scalar @arr instead of rand $#arr. But if that is fixed (and "20" and "200" are changed to match each other), then it is a fair shuffle. However the OP's approach is still inferior to Fisher-Yates in that it has quadratic instead of linear running time (because of the splicing), and it does not shuffle in place like F-Y.

blokhead

Hi tamaguchi, Try this,

  use strict;
  use warnings;
  use Data::Random qw(:all);
   
  my @set = (1..200);  
  my @random_set = rand_set( set => \@set, size => $#set );  
  $,="\n";  
  print @random_set;
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I recommend a look at the QandASection: arrays section of Categorized Questions and Answers:

• How do I pick a random element from an array?
• How do I shuffle an array?

Super Search is your friend:

• randomize array
• Array Shuffle
• Randomising the order of an array

... and so on.

HTH,

The best way to unsort an array? Sort it!!

@a=0..20;$,=" ";
print sort {1-int rand 3} @a;
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If this is for a class project or a nuclear power plant I wouldn't do it this way:

@a = (0..20);$,="\n";
for(0..200){$b=shift @a;push @a,(int rand 2)?($b,shift @a):(shift@a,$b
+)}
print @a;
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