Hi Kenneth,
2009/10/28 Lettow, Kenneth <[email protected]>:
> The equivalent phrase is:
> CO=: ({...@] <: [)*.([ < {:@])
> A quick test shows that it is faster and almost as lean.
> ...
Thank you for pointing out this, and strange that CO is so
much faster. Would anybody knowledgeable explain why?
As for ‘lean’ … well, CO is a direct expression of what is wanted
(y1<=x and x<y2), so nothing to be surprised of. Plus, it needs
operations for explicitly (albeit tacitly) accessing each of x, y1
and y2, including extracting y1 and y2 from a vector. I wouldn't
– in an array language – call this lean :) In fact, it would have
been more straightforward to express the same in C.
The first variant I came up was
w1=. (>:{.)*.(<{:)
which is not unlike CO but simpler. Then I had
w2=. (<{.)<(<{:)
which is simpler yet. I was finally satisfied with
w3=. </@:<
Each of w1, w2, and w3 is simpler than CO, and w1 and w2
are as fast. Only w3 is slower, for a reason that is mysterious
to me.
I should also add that, in case it is not known which end of the
interval is the lower one, we could use a very similar verb:
w4=. ~:/@:<
in place of w3.
2.4 (~:/@:<) 2 3
1
2.4 (~:/@:<) 3 2
1
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