R name colnames and rownames in list of data.frames with lapply

Question

I\'m pretty frustrated because I dont know how I achieve the naming of the columns and rows in a list of data.frames. I mean I want to avoid using a loop. So I figured I cou

Answer 1

I'll prefer setNames in this case

set.seed(1)
datalist <- list(dat1 = data.frame(A = 1:10, B = rnorm(10)),
                 dat2 = data.frame(C = 100:109, D = rnorm(10))
                 )
lapply(datalist, names)
##  $dat1
## [1] "A" "B"

## $dat2
## [1] "C" "D"

datalist <- lapply(datalist, setNames, paste0("col", 1:2))
lapply(datalist, names)
## $dat1
## [1] "col1" "col2"

## $dat2
## [1] "col1" "col2"

EDIT

A more general solution to modify rownames and colnames within a list

lapply(datalist, "colnames<-", paste0("col", 1:2))
lapply(datalist, "rownames<-", letters[1:10])

Answer 2

You need to remember that the object x inside the lapply is not the original object, but a copy. Changing the colnames of the copy does not impact the original object. You need to return x in order to get a new copy of the object that includes the new names.

new_obj = lapply(a, function(x) {
   colnames(x) <- paste("col",1:10,sep="")
   return(x)
  })