I'm trying to find the most economical and elegant code for a simple task: fill an empty matrix with randomly sampled values (here, A, B, or C). For illustration, let's take this matrix:

```
x <- matrix(NA, nrow=8, ncol=4)
[,1] [,2] [,3] [,4]
[1,] NA NA NA NA
[2,] NA NA NA NA
[3,] NA NA NA NA
[4,] NA NA NA NA
[5,] NA NA NA NA
[6,] NA NA NA NA
[7,] NA NA NA NA
[8,] NA NA NA NA
```

To fill it I've used two codes so far, each successfully doing the job. The first uses `sapply`

:

```
x[] <- sapply(x, function(i) sample(LETTERS[1:3], 1, replace = F))
x
[,1] [,2] [,3] [,4]
[1,] "C" "A" "B" "C"
[2,] "B" "B" "B" "B"
[3,] "A" "B" "B" "B"
[4,] "B" "C" "A" "C"
[5,] "B" "A" "C" "A"
[6,] "A" "B" "C" "A"
[7,] "A" "C" "C" "A"
[8,] "C" "B" "B" "C"
```

while the second is a `for`

loop:

```
for(i in 1:nrow(x)){
x[i,] <- sample(LETTERS[1:3], 4, replace = T)
}
x
[,1] [,2] [,3] [,4]
[1,] "C" "A" "C" "C"
[2,] "C" "A" "B" "B"
[3,] "C" "C" "A" "B"
[4,] "C" "C" "A" "C"
[5,] "A" "C" "C" "C"
[6,] "B" "C" "A" "A"
[7,] "C" "C" "B" "A"
[8,] "B" "C" "B" "C"
```

I like neither of them as they both look bulky. Is there a better way to get the expected result, that is, is there a shorter and/or more elegant way?