[Haskell-cafe] How to improve its performance ?

[Ozgur Akgun]

As Daniel pointed out earlier, this may be of a little bit of help:

http://haskell.org/ghc/docs/latest/html/libraries/base-4.2.0.0/src/Data-List.html#subsequences



On 18 March 2010 04:03, Alexander Solla <ajs at 2piix.com> wrote:

>
> On Mar 17, 2010, at 8:33 PM, zaxis wrote:
>
>
>> `allPairs list = [(x,y) | x <- list, y <- list]  ` is not what
>> `combination`
>> does !
>>
>>> let allPairs list = [(x,y) | x <- list, y <- list]
>>> allPairs [1,2,3]
>>>
>> [(1,1),(1,2),(1,3),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)]
>>
>
> Yeah, I know that.  I said so specifically.  combination computes the power
> set of a list.  You said your goal was to compute a set of "two groups".
>  You don't need the power set in order to compute a set of pairs.  Moreover,
> computing the power set is a slow operation.  Indeed, it is the source of
> your slowness.
>
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-- 
Ozgur Akgun
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