Filling matrices with NA to meet desired dimensions - r

Question

I have a list of matrices that I've created. The matrices in the list have different dimensions, and I would like to fill the matrices that don't have a 3x3 dimension with NAs.
I have included my expected outcome below. I would like to include this in a if statement, where if the matrix in the list doesn't have a 3x3 dimension I would like to added empty columns/rows to those matrices and fill them with an NA. Is there an efficient way of doing this in base r?
# Created Matrices
m1 <- matrix(1:9, 3,3)
m2 <- matrix(1:4, 2,2)
m3 <- matrix(1:3, 3, 1)
# Matrices into a list
l1 <- list(m1, m2, m3)
l1
# Expected Matrices and outputs
m2_new <- matrix(c(1,2,NA,3, 4, rep(NA, 4)), 3,3)
m3_new <- matrix(c(1,2,3,rep(NA, 6)), 3,3)
expected <- list(m1, m2_new, m3_new)

Answer 1

One option would be to create a NA matrix and replace the values with the 'x' based on the row/col index
dummy <- matrix(ncol = 3, nrow = 3)
l2 <- lapply(l1, function(x) replace(dummy, cbind(c(row(x)), c(col(x))), x))
-checking
> all.equal(l2, expected)
[1] TRUE

Answer 2

You can replace parts of a matrix with matrix indexing.
mat <- array(dim = c(3, 3))
lapply(l1, function(x) `[<-`(mat, 1:nrow(x), 1:ncol(x), x))
# [[1]]
# [,1] [,2] [,3]
# [1,] 1 4 7
# [2,] 2 5 8
# [3,] 3 6 9
#
# [[2]]
# [,1] [,2] [,3]
# [1,] 1 3 NA
# [2,] 2 4 NA
# [3,] NA NA NA
#
# [[3]]
# [,1] [,2] [,3]
# [1,] 1 NA NA
# [2,] 2 NA NA
# [3,] 3 NA NA

Answer 3

Update see comment by Darren Tsai:
n <- 3
l2 <- lapply(l1, function(x) rbind(x, matrix(ncol = ncol(x), nrow = n - nrow(x))))
x <- sapply(l2, `length<-`, max(lengths(l2)))
list(m1 = matrix(x[,1],3), m2 = matrix(x[,2],3), m3 = matrix(x[,3],3))
$m1
[,1] [,2] [,3]
[1,] 1 4 7
[2,] 2 5 8
[3,] 3 6 9
$m2
[,1] [,2] [,3]
[1,] 1 3 NA
[2,] 2 4 NA
[3,] NA NA NA
$m3
[,1] [,2] [,3]
[1,] 1 NA NA
[2,] 2 NA NA
[3,] 3 NA NA
First answer: not correct output:
Here is another approach:
x <- t(sapply(l1, `length<-`, max(lengths(l1))))
l2 <- list(x[,1:3], x[,4:6], x[,7:9])
l2
[[1]]
[,1] [,2] [,3]
[1,] 1 1 1
[2,] 1 2 3
[3,] 1 2 3
[[2]]
[,1] [,2] [,3]
[1,] 2 2 2
[2,] 4 NA NA
[3,] NA NA NA
[[3]]
[,1] [,2] [,3]
[1,] 3 3 3
[2,] NA NA NA
[3,] NA NA NA

Answer 4

I think there are better solutions but mine will handle a 1x1 matrix as well, which is really just a vector.
You can use the function I've made here resize_matrix in your code however you'd like. It is pretty verbose, but I thinks it's easy to understand exactly what it's doing under the hood. Note: the function is meant to be used in an lapply() call.
The input:
m1 <- matrix(1:9, 3,3)
m2 <- matrix(1:4, 2,2)
m3 <- matrix(1:3, 3, 1)
m4 <- matrix(1:3, 1, 3)
m5 <- matrix(1, 1, 1)
# Matrices into a list
l1 <- list(m1, m2, m3, m4, m5)
l1
#> [[1]]
#> [,1] [,2] [,3]
#> [1,] 1 4 7
#> [2,] 2 5 8
#> [3,] 3 6 9
#>
#> [[2]]
#> [,1] [,2]
#> [1,] 1 3
#> [2,] 2 4
#>
#> [[3]]
#> [,1]
#> [1,] 1
#> [2,] 2
#> [3,] 3
#>
#> [[4]]
#> [,1] [,2] [,3]
#> [1,] 1 2 3
#>
#> [[5]]
#> [,1]
#> [1,] 1
The function:
resize_matrix <- function(mat, desired_rows = 3, desired_columns = 3){
needed_cols <- desired_columns - dim(mat)[2]; needed_cols
needed_rows <- desired_rows - dim(mat)[1]; needed_rows
if (dim(mat)[1] == 1 & dim(mat)[2] == 1){
# we're give a matrix with a single value, expand correctly
final_mat <- matrix(NA, nrow = desired_rows, ncol = desired_columns)
final_mat[1,1] <- mat
} else if (needed_cols > 0 & needed_rows > 0){
# we need to add both rows and columns
col_res <- rep(NA, needed_rows)
row_res <- rep(NA, needed_cols)
mat_temp1 <- rbind(mat, col_res)
final_mat <- unname(cbind(mat_temp1, row_res))
} else if (needed_cols > 0 & needed_rows == 0) {
# we need to add only columns
row_res <- matrix(rep(NA, needed_cols),
ncol = needed_cols, nrow = desired_rows)
final_mat <- unname(cbind(mat, row_res))
} else if (needed_cols == 0 & needed_rows > 0) {
# we need to add only rows
col_res <- matrix(rep(NA, needed_rows),
ncol = desired_columns, nrow = needed_rows)
final_mat <- unname(rbind(mat, col_res))
} else {
# we don't need to add anything, return the matrix
final_mat <- mat
}
return(final_mat)
}
The output:
lapply(l1, FUN = resize_matrix)
#> [[1]]
#> [,1] [,2] [,3]
#> [1,] 1 4 7
#> [2,] 2 5 8
#> [3,] 3 6 9
#>
#> [[2]]
#> [,1] [,2] [,3]
#> [1,] 1 3 NA
#> [2,] 2 4 NA
#> [3,] NA NA NA
#>
#> [[3]]
#> [,1] [,2] [,3]
#> [1,] 1 NA NA
#> [2,] 2 NA NA
#> [3,] 3 NA NA
#>
#> [[4]]
#> [,1] [,2] [,3]
#> [1,] 1 2 3
#> [2,] NA NA NA
#> [3,] NA NA NA
#>
#> [[5]]
#> [,1] [,2] [,3]
#> [1,] 1 NA NA
#> [2,] NA NA NA
#> [3,] NA NA NA
Created on 2022-04-16 by the reprex package (v2.0.1)