Mikl Kurkov wrote:
> I have task for which I couldn't find a solution.
Some background about the larger problem into which this fits
might be useful?
> Suppose we have some indexes which relate to some data.
> Now I have vector which describe which indexes to keep
> and which to remove.
>
> For example: pat =: 4 _3 2 _1
Without knowing more about the problem, "indices" seems like
it might just as well be "values".
> Positive value - tell how many indexes to keep, negative to remove.
> So the pat is telling that I need to keep 4 first indexes then
> remove 3 next, keep another 2, remove 1, keep 4, remove 3 and so on.
> I need function that for giving index give me new index after
> applying such pattern. Indexes of removed items - is index of next
> keeped item.
>
> So applying this function to i.20 and pat I should see:
> OLD: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
> NEW: 0 1 2 3 4 4 4 4 5 6 6 7 8 9 10 10 10 10 11 12
So the pattern repeats?
First off, consider:
shift=: _1 |.!.0 ]
+/\ shift (|#0<])4 _3 2 _1
0 1 2 3 4 4 4 4 5 6
You can get the above from:
+/\ shift (|#0<])4 _3 2 _1 4 _3 2 _1
0 1 2 3 4 4 4 4 5 6 6 7 8 9 10 10 10 10 11 12
To get what I think you are asking for, you need to extend the
pattern to the proper length.
To get the more general result, I guess you would use the above as
a left argument to { but I may have misunderstood what you are
asking for.
It seems to me that given a list of length n and a pattern p, that
you want >.n%+/|p copies of the pattern. This will sometimes give
you a set of indices which are too long, so use n{. after generating
the sequence of indices.
--
Raul
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