Question

How would I create a matrix (the normal sense, not the R sense) where the (i,j) entry is a function of i and j? I think it involves apply() but I can’t seem to work out how to use it.

Say if I have columns x1, x2, … and rows y1,y2 where the x1 and y1 are R objects and I want to build a table/matrix where the entry is a function of xi and yj for each i and j.

Sorry if this has been answered elsewhere.

Answer 1

I’m not sure I understand the entire question. I will just answer the question in the first sentence:

fun <- function(i,j) i*j

rows <- 1:5
cols <- 1:3

outer(rows,cols,FUN=fun)

     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    2    4    6
[3,]    3    6    9
[4,]    4    8   12
[5,]    5   10   15