# [R] expand a matrix

Jinsong Zhao j@zh@o @end|ng |rom ye@h@net
Tue Sep 6 04:45:38 CEST 2022

```Hi there,

I have a matrix likes:
> m
[,1] [,2] [,3] [,4]
[1,]   NA    1    2    3
[2,]    1   NA    6    5
[3,]    2    6   NA    4
[4,]    3    5    4   NA

I hope to expand it to 10 by 10 matrix, M, likes:
> M
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]   NA   NA   NA   NA    1    1    2    3    3     3
[2,]   NA   NA   NA   NA    1    1    2    3    3     3
[3,]   NA   NA   NA   NA    1    1    2    3    3     3
[4,]   NA   NA   NA   NA    1    1    2    3    3     3
[5,]    1    1    1    1   NA   NA    6    5    5     5
[6,]    1    1    1    1   NA   NA    6    5    5     5
[7,]    2    2    2    2    6    6   NA    4    4     4
[8,]    3    3    3    3    5    5    4   NA   NA    NA
[9,]    3    3    3    3    5    5    4   NA   NA    NA
[10,]    3    3    3    3    5    5    4   NA   NA    NA

I use the following code:

M <- matrix(NA, 10, 10)

for (i in 1:10) {
for (j in 1:10) {
if (i %in% 1:4 & j %in% 5:6) M[i,j] <- M[j,i] <- m[1,2]
if (i %in% 1:4 & j == 7) M[i,j] <- M[j,i] <-m[1,3]
if (i %in% 1:4 & j %in% 8:10) M[i,j] <- M[j,i] <-m[1,4]
if (i %in% 5:6 & j == 7) M[i,j] <- M[j,i] <-m[2,3]
if (i %in% 5:6 & j %in% 8:10) M[i,j] <- M[j,i] <-m[2,4]
if (i == 7 & j %in% 8:10) M[i,j] <- M[j,i] <-m[3,4]
}
}

Is there any convenience way to do it? Thanks!

Best,
Jinsong

```