hxd1011 - 1 month ago 5

R Question

Suppose I have a function return 2 matrices. For each input i.

`f<-function(i){`

m1=matrix(i,ncol=5,nrow=5)

m2=matrix(i*10,ncol=5,nrow=5)

r=list(m1=m1,m2=m2)

return(r)

}

d=lapply(1:3,f)

How can I get following 2 things without for loop?

`d[[1]]$m1+d[[2]]$m1+d[[3]]$m1`

d[[1]]$m2+d[[2]]$m2+d[[3]]$m2

I tried

`sum(lapply(1:3,function(x) (d[[x]]$m1)))`

Answer

You can use `Reduce`

:

```
Reduce("+", lapply(d, function(x) x$m1))
```

You can also get both `m1`

and `m2`

using `transpose`

, `map`

and `reduce`

from the purrr package:

```
library(purrr)
map(transpose(d), reduce, `+`)
```

This returns:

```
$m1
[,1] [,2] [,3] [,4] [,5]
[1,] 6 6 6 6 6
[2,] 6 6 6 6 6
[3,] 6 6 6 6 6
[4,] 6 6 6 6 6
[5,] 6 6 6 6 6
$m2
[,1] [,2] [,3] [,4] [,5]
[1,] 60 60 60 60 60
[2,] 60 60 60 60 60
[3,] 60 60 60 60 60
[4,] 60 60 60 60 60
[5,] 60 60 60 60 60
```

Source (Stackoverflow)

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