Re: [Gretl-devel] Preserve row and col names of a matrix after functions

A[,{1,-2}] Flag an error, perhaps? Yes,

A <- matrix(1:12,nrow=3) A[,c(1,-2)] # c(1,2) is R for {1,2}

a = 1:12 a[c(1,-2)]

a[c(0,1)]

On Thu, 3 Nov 2016, Berend Hasselman wrote: >>> First, it would be an improvement. Second, if at all possible, I would >>> favor some clever extension of the matrix indexing apparatus. For >>> example (just an example, no claim of optimality), X[-3, -2] might >>> return the matrix X without the 3rd row and the 2nd column. >> >> I appreciate that you said "no claim of optimality", but I don't think >> we should use negative indices for the purpose you indicate. Seems to >> me the de facto standard regarding negative indices in matrix-oriented >> languages is that they mean, "count from the end, not the beginning", >> not "drop these rows or columns". > > Try this in R: > > A <- matrix(1:12,nrow=3) > A > A[-1,-2] > > displays A without first row and second column. > As I expected and hoped. I normally don't like R very much, but I must admit I find this quite cool. I guess we could adopt the following convention with respect to matrix slicing: positive indices mean "keep" and negative indices mean "drop". My earlier example would just become X[,{-2,-3,-5}], or even X[,-{2,3,5}]. As for the "from the end" convention, I guess that this is (at least in my own experience) a rather unusual case, that can be easily handled via mreverse() or by tricks like # slice columns 1,3 and 4 from the end matrix e = (cols(A) + 1) - {1,3,4} eval A[,e] The "minus is for dropping" convention would have the advantage of being (a) intuitive (b) backwards compatible, though we should decide what to do in the mixed case, eg, A[,{1,-2}] Flag an error, perhaps? ------------------------------------------------------- Riccardo (Jack) Lucchetti Dipartimento di Scienze Economiche e Sociali (DiSES) Università Politecnica delle Marche (formerly known as Università di Ancona) r.lucchetti(a)univpm.it http://www2.econ.univpm.it/servizi/hpp/lucchetti ------------------------------------------------------- _______________________________________________ Gretl-devel mailing list Gretl-devel(a)lists.wfu.edu http://lists.wfu.edu/mailman/listinfo/gretl-devel