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-----Oorspronkelijk bericht----- Van: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] Namens Leigh J. Halliwell Verzonden: dinsdag 24 oktober 2006 17:08 Aan: 'Programming forum' Onderwerp: [Jprogramming] Choose Operators Dear J Forum: I have two questions about selecting, or choosing. 1) There is a m-element vector X whose elements belong to i. n. And there is an (mxn) matrix Y. I want the n-element vector Z whose jth element is (X(j), j). In other words, X tells the rows of the elements to choose from the columns of Y. As an example: X =. 0 2 1 0 Y =. i. 3 4 Then Z =. 0 9 6 3 I believe that I once saw a J primitive that does this; but I can't find it now. 2) X0 and X1 are numeric vectors, and B is a Boolean vector. They all have the same length. I'd like to select from X0 where B is 0, and from X1 where B is 1. I try the expression: X1 [^:B X0 But the adverb ^:B wants to get two-dimensional, i.e., to apply each B to every pair of X1 and X2. How can I make J to apply the adverb one-to-one with the arguments? Thanks. Sincerely, Leigh ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
