Suppose I have the following tibble:

```
library(dplyr)
N <- 100
I <- 5
K <- 10
X <- tidyr::expand_grid(N = 1:N,
I = 1:5,
K = 1:K) %>%
mutate(x = rnorm(n = N*I*K, mean = 5, sd = 2))
```

^{Created on 2021-01-11 by the reprex package (v0.3.0)}

I would like to convert that tibble into a list of `I`

`NxK`

matrices.

I was able to create a list of tibbles as follows, but I would like to convert that into a list of matrices:

```
X2 <- X %>%
tidyr::pivot_wider(names_from = K, values_from = x) %>%
select(-N) %>%
group_by(I) %>%
tidyr::nest() %>%
pull(data)
```

Thanks!