[Gretl-devel] Re: the choose() function

Am 10.06.21 um 10:57 schrieb Riccardo (Jack) Lucchetti: Hi guys, I did not really get the conclusion of this discussion: Do all agree that your choose() function is supposed to become part of the extra package? If so, I have the following comments on it: 1) Nice function. Actually, I just need this for another package I am working on ;-) 2) The name: Why not call it nchoosek() or combinations()? The first suggestion is familiar for people coming from Matlab -- which are not too few. Simply "choose" sounds _too_ general I would say (choose what from which source?). 3) I suggest to change the signature to function matrix choose (matrix from "Set of all choices", int h[1::] "Number of selected choices") First, h must be an integer, right? Second, we have another check that only positive integers are passed. Here is a slightly modified version. <> function matrix choose (matrix from "Set of all choices", int h[1::] "Number of selected choices") /* If "from" is a vector with n elements, this function returns a matrix whose rows are all the possible subsets with h elements; a recursive algorithm is used. # For example: choose({1,2,3}, 2) returns # # 1 2 # 1 3 # 2 3 return: matrix with n! / (h! * (n-h)!) rows if succesful, otherwise 1x1 matrix with an NA value. */ if rows(from) > 1 && cols(from) > 1 s = argname(from) printf "\nError: %s is not a vector\n", strlen(s) ? s : "argument 1" return {NA} endif if h == 1 matrix ret = vec(from) else matrix ret = {} n = nelem(from) loop i=1..(n-h+1) x = from[i] matrix c = from[i+1:] if rows(c) > 0 matrix ret |= x ~ choose(c, h-1) endif endloop endif return ret end function eval choose({1,2,3}, 2) matrix v = seq(1, 10) matrix r = choose(v, 5) eval rows(r) </> If we agree that this shall become part of the extra package, I add 2-3 tests to our test suit for extra. Artur