R creating a binary matrix from information in another matrix-CodePudding

I have a matrix indicating in which column there should be a value 1. All other columns should have a value of 0. For example,

m = matrix(c(3,3,3,5,12,13),nrow = 3)

How should I efficitietly create the following matrix?

     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
[,1]    0    0    1    0    1    0    0    0    0     0     0     0     0     0
[,2]    0    0    1    0    0    0    0    0    0     0     0     1     0     0
[,3]    0    0    1    0    0    0    0    0    0     0     0     0     1     0

Thank you

CodePudding user response：

You can create a matrix of 0's with desired dimensions

out <- matrix(0, nrow = 3, ncol = 14)

Then cbind a vector of row indices with c(m), i.e. column positions

tmp <- cbind(seq_len(3), c(m))

tmp is a matrix that you can use now to replace desired positions with 1

out[tmp] <- 1
out
#         [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
#    [1,]    0    0    1    0    1    0    0    0    0     0     0     0     0     0
#    [2,]    0    0    1    0    0    0    0    0    0     0     0     1     0     0
#    [3,]    0    0    1    0    0    0    0    0    0     0     0     0     1     0

Another, probably less efficient way, could be this

t(apply(m, 1, tabulate, nbins = 14))

CodePudding user response：

Create a matrix of row ids and elements from your original matrix m1 Create a matrix poplulated with zeros with the same number of rows as the original and number of columns one more than the maximium element in the original.



m1 <- matrix(c(rep(1:nrow(m), ncol(m)), as.vector(m)), ncol = 2)

mx <- matrix(0, nrow = 3, ncol = max(m)   1)
mx[m1] <- 1
mx
#>      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14]
#> [1,]    0    0    1    0    1    0    0    0    0     0     0     0     0     0
#> [2,]    0    0    1    0    0    0    0    0    0     0     0     1     0     0
#> [3,]    0    0    1    0    0    0    0    0    0     0     0     0     1     0

^{Created on 2022-03-23 by the reprex package (v2.0.1)}