I suggest that as usual, you should write the expression
in the "best" way, and then wait for the implementation
to catch up.
What might the "best" way be? Perhaps:
({...@[ f ]) *. ({:@[ g ])
where f and g are one of < <: , used as
(a,b) expression x where a and b are atoms
and x is an array. If the interval endpoints
are known, I might write it as (y1&<: *. <&y2) .
If/when the implementation catches up,
the time should be the same as in C and the
space should be optimal (just whatever space
is needed to hold the overall results).
----- Original Message -----
From: Boyko Bantchev <[email protected]>
Date: Wednesday, October 28, 2009 10:13
Subject: Re: [Jprogramming] x ∈ [y1,y2)
To: Programming forum <[email protected]>
> 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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