Roger got it first, but I wrote a little more than he did, so here it
is:
This is a very difficult problem in J, and a reasonably good candidate
for a language primitive. This essay describes a very similar problem
whose solution is slightly more powerful:
http://code.jsoftware.com/wiki/Essays/Progressive_Index-Of
The progressive index-of is related to dyad (i.) in the same way that
the verb you want is related to (-.). The verb (-.) is equivalent to
([ #~ #@] = i.~), and the same relation holds with progressive index-of
and your desired verb. Thus, using (oc) and (pi) from the essay,
oc=: i.~ (] - {) /:@/:
pi=: #@[ ({. i.&(,.oc) }.) [ i. ,
cless =: [ #~ #@] = pi~
'abcabbe' cless 'babe'
cab
I don't find this solution particularly satisfactory since it uses a lot
of data shuffling that is only tangentially related to the actual
computation performed. However, the performance is tolerable: it's
probably a factor of ten off from the speed of a J primitive built for
the task.
Marshall
On Mon, Jan 18, 2016 at 01:19:24PM +0900, June Kim (김창준) wrote:
> Hello
>
> I am looking for a verb(cless) that does something similar to Less(-.) but
> counting the elimination, for example:
>
> 'abcabbe' -. 'abbe'
>
> c
>
> 'abcabbe' cless 'babe' NB. get rid of y letters counting the occurrences
>
> 'cab'
>
>
> It is easier to define such a verb recursively: 'abcabbe' cless 'babe'
> equald to 'e' cless~ 'b' cless~ 'a' cless~ 'b' cless~ 'abcabbe'
>
>
> I think recursive definition isn't a usual J-ic approach.
>
>
> How would you implement such a verb elegantly(with which I mean short)?
>
>
> June
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