How to change colnames based on name of the list?

Question

I am learning R and I have a simple question of how to change a specific colnames based on the name of the list. For example, I have a list Combined :

Combined = list(L1 = mtcars[1:3,], L2 = mtcars[11:13,])

I wanted to change the 5th column to "L1" and "L2", respectively, like

$L1
                   mpg cyl  disp  hp   L1    wt  qsec vs am gear carb
Mazda RX4         21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag     21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
Datsun 710        22.8   4 108.0  93 3.85 2.320 18.61  1  1    4    1

$L2
                     mpg cyl  disp  hp   L2    wt  qsec vs am gear carb
Merc 280C           17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
Merc 450SE          16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3
Merc 450SL          17.3   8 275.8 180 3.07 3.730 17.60  0  0    3    3

So I tried

lapply(Combined, function(x) {colnames(x)[5] <- names(x); x}) 

But it did not work. Can anyone help? Thanks!

Answer 1

Here is one option with imap with rename_at . imap uses map2 to return both the value in .x and the names of the list in .y . Then, we just need the position of the column to rename it and this can be done with rename_at (which takes either index or name as string)

library(purrr)
imap(Combined, ~ {nm1 <- .y
           .x %>% 
                rename_at(5,  ~nm1)
    })

---

Or in base R with Map

Map(function(dat, nm) {names(dat)[5] <- nm; dat}, Combined, names(Combined))
#$L1
#               mpg cyl disp  hp   L1    wt  qsec vs am gear carb
#Mazda RX4     21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
#Mazda RX4 Wag 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
#Datsun 710    22.8   4  108  93 3.85 2.320 18.61  1  1    4    1

#$L2
#            mpg cyl  disp  hp   L2   wt qsec vs am gear carb
#Merc 280C  17.8   6 167.6 123 3.92 3.44 18.9  1  0    4    4
#Merc 450SE 16.4   8 275.8 180 3.07 4.07 17.4  0  0    3    3
#Merc 450SL 17.3   8 275.8 180 3.07 3.73 17.6  0  0    3    3

Answer 2

Here is another base R option with lapply

Combined [] <- lapply(
  seq_along(Combined),
  function(k) {
    setNames(
      Combined[[k]],
      replace(names(Combined[[k]]), 5, names(Combined)[k])
    )
  }
)

such that

> Combined
$L1
               mpg cyl disp  hp   L1    wt  qsec vs am gear carb
Mazda RX4     21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
Mazda RX4 Wag 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
Datsun 710    22.8   4  108  93 3.85 2.320 18.61  1  1    4    1

$L2
            mpg cyl  disp  hp   L2   wt qsec vs am gear carb
Merc 280C  17.8   6 167.6 123 3.92 3.44 18.9  1  0    4    4
Merc 450SE 16.4   8 275.8 180 3.07 4.07 17.4  0  0    3    3
Merc 450SL 17.3   8 275.8 180 3.07 3.73 17.6  0  0    3    3