使用 lapply 为数据框列表设置列名？

Question

I'm pretty new to R but I'm trying to create a list of data frames and then give them all the same headers in a loop. The plan is to then fill the columns with data from a bunch of messy data files and then bind the small data frames all a single data frame. However, I'm stuck on assigning the column names. I did first try a for loop but saw other answers saying that was the newbie way to do it.

This is what I have right now but when I run it the columns don't update:

a <- data.frame(matrix(ncol=5, nrow=1))
b <- data.frame(matrix(ncol=5, nrow=1))
c <- data.frame(matrix(ncol=5, nrow=1))
d <- data.frame(matrix(ncol=5, nrow=1))

List <- list(a, b, c, d)
headers <- c("First Name","Last Name","Date","Zip Code", "blah")

lapply(List, setNames, nm = headers)

I think I'm missing something about how data frames are updated in R because I do get a print out of 4 empty data frames with the right column names. So the function is applying to something. But it's not updating my list and I'm failing to understand why.

Thank you!

Answer 1

We can set column names using,

List = lapply(List, function(x) `colnames<-`(x, headers))

Answer 2

It seems you want to update the original dataframes. In that case, your list MUST be named. ie check the code below.

List <- list(a = a, b = b, c = c, d = d)
list2env(lapply(List, setNames, nm = headers), globalenv())

Now if you call a you will note that it has been updated.