Re: Re: Re: Fisher-Yates shuffle?

will turn that around and ask--Why not?--provided it works

Well, i suppose there are different answers. One could be speed. A "normal" swap of two variables (using a temp var and three assignments) is faster than list assignment. Another but better argument is maintainability. Consider that the cause of abigail-IIs concern about the LHS/RHS is that of trying to get the code to work without imposing a scoping block of some sort. Also, another effect of trying to get this to work on one line is that you used $a. Now most would tell you to avoid that and $b for various reasons. In your code it doesnt look like it would be a problem, but as the code morphs in the future, perhaps back to a multiline solution maybe that $a will not go away, and then maybe the code will morph so much that the trap im thinking off catches you (or your successor)

But one liners are fun I agree. :-)

Given Abigail's fix for it's failings, I'm happy to use it, with it's dependancy on subscript evaluation order on the basis that if this ever changes, it will break a lot of other code too, so the change should be well announced.

Actually I doubt it would be. Im pretty sure the assumption would be that no one in their right mind would depend on such an undocumented feature. (er, sorry :-)

Anyway, seya,

Yves / DeMerphq
---
Software Engineering is Programming when you can't. -- E. W. Dijkstra (RIP)

Comment on Re: Re: Re: Fisher-Yates shuffle?

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Re: Re: Re: Re: Fisher-Yates shuffle? by BrowserUk (Patriarch) on Aug 09, 2002 at 22:43 UTC
Just to show I do listen:). As you don't object to $a and do object to slices and the reliance on subscript evaluation order, I offer this: (it passes Abigail-II's test!!) `$_ ne ($a=int( rand( $#values-$_+1))+$_) and $values[$_] ^= $values[$a] ^= $values[$_] ^= $values[$a] for (0..$#values); # Fisher-Yates one-liner` [download] Its a shame you can't use an named iterator with the `for (`list`)` statement modifier otherwise I would have this as: `$b ne ($a=int(rand($#values-$b+1))+$b) and $values[$b] ^= $values[$a] ^= $values[$b] ^= $values[$b] for $b (0..$#values);` [download] Then noone could complain about the use of $a and $b...they are used for swapping aren't they? UpdateI forgot to mention...I had to re-institute the don't swap if same test for this to work, but given some C-compilers used the 3-Xor's trick to optomise register swaps in register constrained situations, I wonder if this was the real reason for that test in the oeriginal Fisher-Yates C code?	[reply] [d/l] [select]

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Re: Re: Re: Re: Fisher-Yates shuffle?
by BrowserUk (Patriarch) on Aug 09, 2002 at 22:43 UTC

Just to show I do listen:).

As you don't object to $a and do object to slices and the reliance on subscript evaluation order, I offer this: (it passes Abigail-II's test!!)

    $_ ne ($a=int( rand( $#values-$_+1))+$_) 
    and $values[$_] ^= $values[$a] ^= $values[$_] ^= $values[$a] 
        for (0..$#values); # Fisher-Yates one-liner
[download]

Its a shame you can't use an named iterator with the for (list) statement modifier otherwise I would have this as:

    $b ne ($a=int(rand($#values-$b+1))+$b) 
    and $values[$b] ^= $values[$a] ^= $values[$b] ^= $values[$b] 
        for $b (0..$#values);
[download]

Then noone could complain about the use of $a and $b...they are used for swapping aren't they?

UpdateI forgot to mention...I had to re-institute the don't swap if same test for this to work, but given some C-compilers used the 3-Xor's trick to optomise register swaps in register constrained situations, I wonder if this was the real reason for that test in the oeriginal Fisher-Yates C code?

[reply]
[d/l]
[select]