My first thought is
slice =. {."1 </.`(~.@[)`(#&a:@>:@(>./)@[)} {:"1
data=:>0 1;0 2;0 3;1 1;1 3;2 1;4 1
slice data
+-----+---+-++-+
|1 2 3|1 3|1||1|
+-----+---+-++-+
I don't know if that's better, or if it was suggested earlier.
Henry Rich
On 5/5/2011 11:06 AM, John Randall wrote:
> I have a set of ordered pairs of nonnegative integers (representing
> pixels that are set in a binary image). To speed up access, I want to
> produce an array s of boxes such that (x,y) is an ordered pair if and
> only if y e. x {:: s . Keys would work perfectly for this except for
> skipped x-values, so I work around it, essentially inserting a bogus
> y-value for every x-value, and then removing it.
>
> data=:>0 1;0 2;0 3;1 1;1 3;2 1;4 1
>
> slice=:3 : 0
> 'X Y'=.|:/:~ y
> m=.>:>./X
> n=.>:>./Y
> X=.(i.m),X
> Y=.(m#n),Y
> -.&n&.> X</.Y
> )
> slice data
> +-----+---+-++-+
> |1 2 3|1 3|1||1|
> +-----+---+-++-+
>
> I also have a test verb.
>
> test=:3 : 0
> y=./:~y
> s=.slice y
> y-:;(<"0 i.#s)(,"_ 0)&.> s
> )
>
> test data
> 1
>
> Does anyone have any suggestions as to how to do this better?
>
> Best wishes,
>
> John
>
>
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