Extracting levels of a factor from column number-R

Question

I have a data.frame (df) with column name v1 which is a factor. Like:

df
# v1
# --
# a
# b
# c

When I want to get levels of the factor I get:

By column name:

levels(df$v1)
# [1] "a" "b" "c"

By column number:

levels(df[1])
# NULL

Why do I get NULL when I use column number.

Thanks a lot.

levels(df[[1]]) should work. df[1] extracts a list with one element df[[1]] extracts the contents — Richard Telford, Apr 03 '16 at 20:57
Why is that? df is not defined as a list. It is defined as data frame in my example. — oercim, Apr 03 '16 at 21:00
data.frames are also/primarily lists. try `is.list(iris)` ;-) — Vincent Bonhomme, Apr 03 '16 at 21:02
Or try `df[,1]`. This means selecting all rows and the first column. — Xiongbing Jin, Apr 03 '16 at 21:03
Thanks a lot. I got the idea. Thanks again for sharing your time. — oercim, Apr 03 '16 at 21:06
Always useful to have a gander at http://stackoverflow.com/questions/1169456/in-r-what-is-the-difference-between-the-and-notations-for-accessing-the — MichaelChirico, Apr 03 '16 at 21:29

score 1 · Accepted Answer · answered Apr 04 '16 at 08:36

1

  levels(df[,1]) 
  [1] "a" "b" "c"

answered Apr 04 '16 at 08:36

Sowmya S. Manian

1 Answers1