R：级别映射表和因子变量标签

Question

I am pretty sure I am missing something here, but how can I get a mapping table of the integer codes and the labels of a factor variable in R?

For example, in the chickwts dataset, I would like the output for the feed variable

1 --> casein
2 --> horsebean
3 --> linseed
4 --> meatmeal
5 --> soybean
6 --> sunflower

I am pretty sure there is a built-in function for this, but I can't find it, and neither levels , nlevels or unclass gives me what I want.

Any suggestions?

Answer 1

The codes are just the index into the levels(...) vector.

with(chickwts,data.frame(code=seq_along(levels(feed)),levels=levels(feed)))
#   code    levels
# 1    1    casein
# 2    2 horsebean
# 3    3   linseed
# 4    4  meatmeal
# 5    5   soybean
# 6    6 sunflower

This is the same result you get with as.integer(...) .

with(chickwts,data.frame(code=as.numeric(unique(feed)),level=unique(feed)))
#   code     level
# 1    2 horsebean
# 2    3   linseed
# 3    5   soybean
# 4    6 sunflower
# 5    4  meatmeal
# 6    1    casein