如何用r中的名称列表重命名多个文件的特定列？

Question

I have a folder of .txt files. I have read the files into a list in R by following command:

filenames <- list.files("/path/to/folder")
datalist = lapply(filenames, function(x)read.table(x, header=T))

Now I want to change the 9th column of each file to the name of file(filename list is the vector of names).

do you have any idea how can I do this by using lapply()? Thanks!

Answer 1

You can change a single column name by position by subsetting colnames and inserting like in the example below.

lst <- list(data.frame('a' = c(1,2,3),
                       'b' = c(3,5,6)),
            data.frame('a' = c(1,2,3),
                       'b' = c(3,5,6)),
            data.frame('a' = c(1,2,3),
                       'b' = c(3,5,6)))

lapply(lst, function(item) {
    colnames(item)[2] <- 'cat'   # This would be 9 if you wanted the 9th column
    return(item)
})

[[1]]
  a cat
1 1   3
2 2   5
3 3   6

[[2]]
  a cat
1 1   3
2 2   5
3 3   6

[[3]]
  a cat
1 1   3
2 2   5
3 3   6