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### functional programming: sort to shuffle

by stefp (Vicar)
 on Sep 03, 2001 at 13:24 UTC Need Help??

It shuffles the parameters list:
sub shuffle { map { @_=sort { int (3*rand)-1 } @_ } 0..5 }
Note that I go thru 6 iterations to get "sufficient" disorder.

-- stefp

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Re: sort to shuffle
by demerphq (Chancellor) on Sep 03, 2001 at 15:06 UTC
Cool idea. stefp++.
Curious if sort could get into a 'never finish' scenario if the right values came up from rand though?
Thought you might like this version of the fisher yates shuffle.
sub fy_shuf{my(\$l,\$c,\$r)=@_;map{\$r=int(rand(\$_+1)); @\$l[\$_,\$r]=@\$l[\$r,\$_]}reverse 0..\$#\$l for 0..\$c||0}; my @a=(1..52); fy_shuf(\@a,5);
UPDATE
Having had a look at japhy home node I borrowed an idea from him and reduced it more. (Oh and I decided that shuffling mutiple times was unecessary.)
sub fy_shuf{my(\$l,\$r)=@_;map{\$r=int(rand(@\$l-\$_+1));@\$l[-\$_,\$r]=@\$l[\$r +,-\$_]}0..\$#\$l};

Yves
--

It really depends on the internal sort algorithm. The "never finish" scenario is not the worse possible one: on some old versions of perl, my shuffle function crashes the perl interpretor :)

That is why this really belongs to the obfuscation category... to answer a remark on the CB.

Anyway, on 5.6, it works fine and dandy.

-- stefp

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