Remove the last column of dataframe in R in a function - r

Question

I need to remove the last column of 10 dataframes, so I decided to put it in lapply(). I wrote a function to remove the col, like below,
remove_col <- function(mydata){
mydata = subset(mydata, select=-c(24))
}
and create a mylist <- (data1, data2.... data10), then I passed lapply as
lapply(mylist, FUN = remove_col)
It did give me a list of the removed dataframe, however, when I checked the original dataframe, the last column is still there.
How should I change the code to change the original dataset?

Answer 1

You need to assign the result of the function call to the input list on the LHS:
mylist <- lapply(mylist, FUN = remove_col)
Had you defined your function with an explicit return value, this might have been more obvious:
remove_col <- function(mydata) {
mydata <- subset(mydata, select=-c(24))
return(mydata) # return the modified list/data frame
}

Answer 2

Instead of hardcoding the column number to remove you can use ncol to remove the last column from each dataframe.
remove_col <- function(mydata){
mydata[, -ncol(mydata)]
}
mylist <- lapply(mylist, remove_col)
To see the changes in the original dataframe you can assign names to list of dataframe and use list2env.
names(mylist) <- paste0('data', seq_along(mylist))
list2env(mylist, .GlobalEnv)

Answer 3

Using base R and lapply, Note, you can remove ", drop = F" from your script if there are more than 2 columns in all dataframes in the list.
> d1
c1 c2
1 1 6
2 2 7
3 3 8
4 4 9
5 5 10
> d2
c1 c2
1 5 10
2 4 9
3 3 8
4 2 7
5 1 6
> mylist <- list(d1, d2)
> mylist
[[1]]
c1 c2
1 1 6
2 2 7
3 3 8
4 4 9
5 5 10
[[2]]
c1 c2
1 5 10
2 4 9
3 3 8
4 2 7
5 1 6
> lapply(mylist, function(x) x[,1:(ncol(x)-1), drop = F] )
[[1]]
c1
1 1
2 2
3 3
4 4
5 5
[[2]]
c1
1 5
2 4
3 3
4 2
5 1
>