To expand on what Sarah and Michael said: if you have a 3d array:
> x<-array(1:4,c(2,2,4)) > x , , 1 [,1] [,2] [1,] 1 3 [2,] 2 4 , , 2 [,1] [,2] [1,] 1 3 [2,] 2 4 , , 3 [,1] [,2] [1,] 1 3 [2,] 2 4 , , 4 [,1] [,2] [1,] 1 3 [2,] 2 4 > apply(x,c(1,2),sum) [,1] [,2] [1,] 4 12 [2,] 8 16 a margin of c(1,2) makes more sense. Hope that clarifies things. Justin On Wed, Nov 16, 2011 at 12:18 PM, Sarah Goslee <sarah.gos...@gmail.com> wrote: > Hi, > > On Wed, Nov 16, 2011 at 3:13 PM, <rkevinbur...@charter.net> wrote: >> >> I have the following scenario: >> >>> m <- matrix(1:4, ncol=2) >>> m >> [,1] [,2] >> [1,] 1 3 >> [2,] 2 4 >>> apply(m, 2, sum) >> [1] 3 7 >>> apply(m, 1, sum) >> [1] 4 6 >> >> So I can apply to rows *or* columns. According to the documentation >> (?apply) >> >> MARGIN a vector giving the subscripts which the function will be applied >> over. E.g., for a matrix 1 indicates rows, 2 indicates columns, c(1, 2) >> indicates rows and columns. Where X has named dimnames, it can be a >> character vector selecting dimension names. >> >> >> But I get the following results: >> >>> apply(m, c(1,2), sum) >> [,1] [,2] >> [1,] 1 3 >> [2,] 2 4 >> >> How am I to interpret this result? > > I'm pretty sure R is taking the sum of m[1,1] and putting it [1,1], > and the sum of m[1,2] and putting it in [1,2] and so on. You > instructed apply() to work on rows and columns *simultaneously*, > rather than sequentially. > > apply() on c(1,2) is useful if you have a matrix that's three-dimensional, > but not so much if it's two dimensional. > > What are you trying to accomplish? > > Sarah > > > > > -- > Sarah Goslee > http://www.functionaldiversity.org > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.