Question

I have an empty matrix m:

m <- matrix(0, nrow = 4, ncol = 2, byrow = TRUE,
            dimnames = list(c("sp1", "sp2", "sp3", "sp4"),
                            c("x", "y")))

And need to fill the matrix using the data frame d

d <- data.frame(site = c("x", "y", "u", "v"), 
                species = c("sp1", "sp1", "sp1", "sp1"), 
                freq = c(0.2, 0.3, 0.5, 0.1))

so that if rowname(m) is equal to d[, "species"] and m[, "x"] is equal to the d[, "site"] then d[, "freq"] in entered in the correct place in matrix m i.e. returning:

m <- matrix(c(0.2, 0, 0, 0, 0, 0, 0, 0), nrow = 4, ncol = 2, byrow = TRUE, 
            dimnames = list(c("sp1", "sp2", "sp3", "sp4"),
                            c("x", "y")))

I have tried:

m[d[, c("species", "x")]] <- d[, "freq"]

I suspect I am not doing the data frame indexing properly? Any ideas? Thanks.

Answer 1

That is probably not the best way to do it but this is working:

for(i in 1:nrow(d)){m[rownames(m)==d[i,2],colnames(m)==d[i,1]] <- d[i,3]}