Replace Values of a Large Matrix in R

Question

I have a large matrix (50 X 10,000) that contains integers representing the indices of vector values. I want to replace the integers representing the indices of vector values in the matrix with the actual vector values of the indices.

Here is the vector dat.full$year.total of values:

 [19] 13.51 20.56 20.03 18.33 24.30 19.65 13.99 18.84 18.61 18.70 18.39 13.80 25.89 13.08 17.19 17.90 19.44 20.51
 [37] 21.22 15.98 14.23 11.85 16.08 14.02 16.44 20.25 15.58 29.09 11.11 20.29 23.99 26.23 15.75 18.65 22.65 18.64
 [55] 22.70 17.11 21.22 14.16 27.41 17.15 16.01 10.91 15.25 18.45 27.43 19.28 18.85 15.30 22.39 12.77 16.95 11.47
 [73] 19.47 11.13 24.89 16.19 27.52 16.65 18.69 18.43 20.21 15.11 18.24 14.66 13.49 23.82 24.20 13.45 16.91 21.54
 [91] 24.51 18.54 17.44 21.35 25.82 16.95 20.62 21.70 21.17 17.38 21.87 16.79 29.93 21.38 28.49 22.29 25.88 15.96
[109] 18.28 13.88 22.02 27.17 17.52 19.31 17.13 17.02 22.19 20.32 22.29 15.65 34.15 23.57 27.39 17.25 21.89 19.01
[127] 15.89

The indices are 1 to 127. I tried using replace() like mat<-matrix(replace(mat, row(dat.full), dat.full$year.total)) but this only gives a 1-column matrix. How do I achieve the desired replacements?

Thanks!

Answer 1

Suppose your matrix and vector looked like this:

mat <- matrix(9:1, ncol = 3)
vec <- as.numeric(mat * 20)/100

mat
#>      [,1] [,2] [,3]
#> [1,]    9    6    3
#> [2,]    8    5    2
#> [3,]    7    4    1

vec
#> [1] 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2

Then you simply do:

mat[] <- vec[mat]

So now mat looks like this, with each element replaced by the corresponding entry in vec

mat
#>      [,1] [,2] [,3]
#> [1,]  0.2  0.8  1.4
#> [2,]  0.4  1.0  1.6
#> [3,]  0.6  1.2  1.8