thank you Simon. I find a[M] working to be unexpected, but consistent with (a close reading of) Extract.Rd
Can we reproduce a[,M]? [I would expect this to extract a[,j,k] where M[j,k] is TRUE] try this: > a <- array(1:30,c(3,5,2)) > M <- matrix(1:10,5,2) %% 3==1 > a[M] [1] 1 4 7 10 11 14 17 20 21 24 27 30 This is not doing what I would want a[,M] to do. I'll checkout afill() right now.... best wishes Robin On Wed, Sep 28, 2011 at 10:39 AM, Simon Knapp <sleepingw...@gmail.com> wrote: > a[M] gives the same as your `cobbled together' code. > > On Wed, Sep 28, 2011 at 6:35 AM, robin hankin <hankin.ro...@gmail.com> > wrote: >> >> hello everyone. >> >> Look at the following R idiom: >> >> a <- array(1:30,c(3,5,2)) >> M <- (matrix(1:15,c(3,5)) %% 4) < 2 >> a[M,] <- 0 >> >> Now, I think that "a[M,]" has an unambiguous meaning (to a human). >> However, the last line doesn't work as desired, but I expected it >> to...and it recently took me an indecent amount of time to debug an >> analogous case. Just to be explicit, I would expect a[M,] to extract >> a[i,j,] where M[i,j] is TRUE. (Extract.Rd is perfectly clear here, and R >> is >> behaving as documented). >> >> The best I could cobble together was the following: >> >> ind <- which(M,arr.ind=TRUE) >> n <- 3 >> ind <- >> cbind(kronecker(ind,rep(1,dim(a)[n])),rep(seq_len(dim(a)[n]),nrow(ind))) >> a[ind] <- 0 >> >> >> but the intent is hardly clear, certainly compared to "a[M,]" >> >> I've been pondering how to implement such indexing, and its >> generalization. >> >> Suppose 'a' is a seven-dimensional array, and M1 a matrix and M2 a >> three-dimensional array (both Boolean). Then "a[,M1,,M2]" is a >> natural generalization of the above. I would want a[,M1,,M2] to >> extract a[i1,i2,i3,i4,i5,i6,i7] where M1[i2,i3] and M[i5,i6,i7] are >> TRUE. >> >> One would need all(dim(a)[2:3] == dim(M1)) and all(dim(a)[5:7] == >> dim(M2)) for consistency. >> >> Can any R-devel subscribers advise? >> >> >> >> >> -- >> Robin Hankin >> Uncertainty Analyst >> hankin.ro...@gmail.com >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel > > -- Robin Hankin Uncertainty Analyst hankin.ro...@gmail.com ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
