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.

Answer 1

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