CODEWITHSUNDEEP
arraysrmatrixindexing
needRhelp
needRhelp

Reputation: 3138

Replace matrix values for each array element

I have a 3-dimensional array arr where each array element is a matrix with the same number of rows and columns. Then I have a 3-column matrix m where the first two columns specify an index (row and column) and the last column a value. 

arr = array(0, dim = c(2, 2, 3))
m = matrix(c(1, 2, -100, 2, 1, -99), ncol = 3, byrow = TRUE)
colnames(m) = c("row_index", "column_index", "value")

Now I want to fill in this value at the specified indexes for each of the array elements. I couldn't find a better way to do this than the following lines of code, but I would prefer a solution with less code repetition. What's the best way to do this?

arr[, , 1][m[, 1:2]] = m[, 3]
arr[, , 2][m[, 1:2]] = m[, 3]
arr[, , 3][m[, 1:2]] = m[, 3]

Upvotes: 3

Views: 742

Answers (1)

talat
talat

Reputation: 70266

How about this apply approach:

arr[] <- apply(arr, 3, FUN = function(x) {x[m[,1:2]] <- m[,3]; x})

arr
# , , 1
# 
# [,1] [,2]
# [1,]    0 -100
# [2,]  -99    0
# 
# , , 2
# 
# [,1] [,2]
# [1,]    0 -100
# [2,]  -99    0
# 
# , , 3
# 
# [,1] [,2]
# [1,]    0 -100
# [2,]  -99    0

Upvotes: 4

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