R - convert data.frame to multi-dimensional matrix

Question

From example from a data.frame:

x = data.frame(c(1,1,2,2,3,3), c(1,2,1,2,1,2), c(1,1,1,2,2,2), c(12,14,22,24,34,28))
colnames(x)=c(\"Store\",\"Dept\",\"Year\",\"         


        

Answer 1

Something like :

tapply(X = x[["Sales"]], INDEX = x[setdiff(names(x), "Sales")], FUN = identity)

could work, but it is a bit strange to use tapply with the identity function.

Answer 2

Are you, perhaps, looking for xtabs?

xtabs(Sales ~ Store + Dept + Year, x)
# , , Year = 1
# 
#      Dept
# Store  1  2
#     1 12 14
#     2 22  0
#     3  0  0
# 
# , , Year = 2
# 
#      Dept
# Store  1  2
#     1  0  0
#     2  0 24
#     3 34 28

Answer 3

You have to construct the array before with the appropriate dimension :

Sales <- array(NA, c(max(x$Store), max(x$Dept), max(x$Year)))

and then fill in the data :

for (i in 1:nrow(x)) 
    Sales[x[i,"Store"], x[i,"Dept"], x[i,"Year"]] <- x[i, "Sales"]

Sales[35,71,1]