APLDN Forum

Re 13 & 14: Unless the left- and right- arguments are conformable AND are both vectors, the Dyalog built-in function does not work.

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      a←1 4⍴2 1 3 4
      b←6 2 10 0 10
      a∩b
RANK ERROR
      a∩b
     ∧

I think that a user-defined function is more expedient than a built in function in that the developer can control both the conformance of the arguments and the rank/shape of the result.

Ajay Askoolum wrote:I think that a user-defined function is more expedient than a built in function in that the developer can control both the conformance of the arguments and the rank/shape of the result.

Since Union and Intersection are mathematically "set" operations, and sets are just lists of objects, I can't think why you'd want these defined for anything but vectors (and scalars). I can't think of any reasonable meaning or procedure for using these with matrices. Even if you wanted them done line-by-line you could split it into a vector of vectors for eaching and mix them back together again in-line at least as easily as building a separate function.