In my data block, I define a two-dimensional array of matrices called `X`

. For example:

`matrix[4, 12] X[1000, 9];`

Each of the 1000 respondents go through 9 trials, and information about these trials are stored in a matrix with 4 rows and 12 columns.

How do I create an object in R that represents what Stan is looking for? If you make a two-dimensional array, you cannot assign an element of it to be a matrix:

```
> (test <- array(dim = c(3, 4)))
[,1] [,2] [,3] [,4]
[1,] NA NA NA NA
[2,] NA NA NA NA
[3,] NA NA NA NA
> test[1, 1] <- matrix(1:4, ncol = 2)
Error in test[1, 1] <- matrix(1:4, ncol = 2) :
number of items to replace is not a multiple of replacement length
```

How do I make a two-dimensional array filled with matrices in R, in the format that Stan wants?