I have two adjacency matrices where the second one has some missing data (that means these two matrices are of different square size) but how do I pad the missing data with NA in the second matrix?

Data below:

```
#first matrix
t1 = matrix(
c(1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 0, 1),
nrow = 4,
ncol = 4,
byrow = TRUE
)
rownames(t1) <- c("a","b", "c", "d")
colnames(t1) <- c("a","b", "c", "d")
#second matrix
t2 = matrix(
c(1, 1, 0, 0, 0, 1, 0, 0, 1),
nrow = 3,
ncol = 3,
byrow = TRUE
)
rownames(t2) <- c("a","c", "d") #assume data from b are missing here
colnames(t2) <- c("a","c", "d")
```

Expected outcome for the second matrix:

```
a b c d
a 1 NA 1 0
b NA NA NA NA
c 0 NA 0 1
d 0 NA 0 1
```

I have a much larger dataset and so a more efficient approach will be appreciated@

### >Solution :

If row and column names can be relied upon:

```
t3 <- t1
t3[] <- NA
t3[rownames(t2), colnames(t2)] <- t2
t3
# a b c d
# a 1 NA 1 0
# b NA NA NA NA
# c 0 NA 0 1
# d 0 NA 0 1
```