Say I have three lists:

```
l_zero
[[1]]
[,1] [,2]
[1,] 0 0
[2,] 0 0
[[2]]
[,1] [,2]
[1,] 0 0
[2,] 0 0
l_ind <- list(matrix(c(1,1), ncol = 2), matrix(c(1,1,1,2), ncol = 2))
l_ind
[[1]]
[,1] [,2]
[1,] 1 1
[[2]]
[,1] [,2]
[1,] 1 1
[2,] 1 2
l_val <- list(5, c(4, 7))
l_val
[[1]]
[1] 5
[[2]]
[1] 4 7
```

I would like to run `Map`

over the three lists with the goal of replacing in `l_zero`

the zeros with the coordinates in `l_ind`

with the values from `l_val`

. My attempt gives me the following:

```
Map(function(l_zero, l_ind, l_val) l_zero[l_ind] <- l_val, l_zero = l_zero, l_ind = l_ind, l_val = l_val)
[[1]]
[1] 5
[[2]]
[1] 4 7
```

As you can see, the original dimensions of the matrices are reduced, but I would like to keep the dimensions of the matrices and just replace the values with the coordinates in `l_ind`

. I tried `l_zero[l_ind, drop = FALSE]`

, but that didn't help either.

Can someone help me with this?

Answer:

Here's a bit simpler method, The `[<-`

replacement function can be used in `Map()`

's function argument. It takes three arguments, in order.

```
Map("[<-", l_zero, l_ind, l_val)
# [[1]]
# [,1] [,2]
# [1,] 5 0
# [2,] 0 0
#
# [[2]]
# [,1] [,2]
# [1,] 4 7
# [2,] 0 0
```

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