In R one can use the `<<-` symbol within the `lapply()` function to assign a value to a variable outside `lapply()`.

Let's consider a matrix full of 1:

```
m<-matrix(data=1, nrow=5, ncol=5)

```

Let's say I want to replace each row by the values 1,2,3,4 and 5 using the assignation symbol `<<-`. I can use the function the lapply function (it is not the designed function for that kind of operation, this is only an example):

```
lapply(X = seq(nrow(m)), FUN = function(r){
  m[r,]<<-seq(5)
})

```

This will work.

But if I now use mclapply like this:

```
mclapply(X = seq(nrow(m)), FUN = function(r){
  m[r,]<<-seq(5)
})

```

The matrix m will remain full of 1.

The idea is to apply changes to rows of a matrix, without creating a new one, but rather assigning them in the existing one. The only constrain is to use a function from the parallel package (e.g. mclapply(), but maybe another function would better fit).  

Also using the `<<-` symbol is not mandatory.  

How can I do that ?