N.Varela - 25 days ago 4x

R Question

I want to sum multiple columns of matrices in a list and only show the sum without showing the (calculation) input columns (similar to my former question on data frames). Thanks for the former answers, however I struggled to implement the ideas on matrices. Here an example:

`ls <- list(matrix(c(1, 5, 3, 2), ncol=4), matrix(c(NA, 2, 7, 9), ncol=4))`

countries <- c("a", "b", "c", "d")

ls <- lapply(ls, "colnames<-", countries)

my expected result is:

`[[1]]`

c new

[1,] 3 8

[[2]]

c new

[1,] 7 11

Any ideas how to do this column summation? Thanks

Answer

Try below:

```
calc <- c("a", "b", "d")
keep <- "c"
lapply(ls, function(i){
cbind(i[, keep, drop = FALSE],
new = rowSums(i[, calc, drop = FALSE], na.rm = TRUE))
})
```

Source (Stackoverflow)

Comments