And here it is! Certifiably faster than the naive version.
sortbox =: </. /: ~.@[
bwt =: 3 :'y{~ (([: ; $:^:(1<#)&.>)@:sortbox~ y{~(#y)&|)&.:>: i.@
#y=.y,EAV'
bwt 'aba'
�baa
f=. a.{~ 97+20000?@$26
6!:2 'bwt f'
0.0843269
bwt0=:{:"1@/:~@(|."0 1~ i.@-@#)@(,&EAV)
6!:2 'bwt0 f'
0.976645
Marshall
On Thu, Sep 8, 2011 at 2:59 PM, Marshall Lochbaum <[email protected]>wrote:
> I just realized this. I'm working on a radix-sort-ish method that actually
> performs the correct transform now.
>
> Marshall
>
>
> On Thu, Sep 8, 2011 at 2:57 PM, Raul Miller <[email protected]> wrote:
>
>> On Thu, Sep 8, 2011 at 2:41 PM, Marshall Lochbaum <[email protected]>
>> wrote:
>> > The forward transform can be implemented as:
>> >
>> > bwt =: (/: 1&|.)@:(,&EAV)
>>
>> bwt=: (/: 1&|.)@:(,&EAV)
>> bwt0=:{:"1@/:~@(|."0 1~ i.@-@#)@(,&EAV)
>> (bwt -: bwt0) 'aba'
>> 0
>> bwt 'aba'
>> b�aa
>> bwt0 'aba'
>> �baa
>>
>> --
>> Raul
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>>
>
>
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