How to create a new variable in a data.frame based on a condition?

Question

Assume we have a dataframe

x   y
1   1
2   4 
4   5 

how can you add a new variable to the dataframe such that if x is less than or equal

Answer 1

If you have a very limited number of levels, you could try converting y into factor and change its levels.

> xy <- data.frame(x = c(1, 2, 4), y = c(1, 4, 5))
> xy$w <- as.factor(xy$y)
> levels(xy$w) <- c("good", "fair", "bad")
> xy
  x y    w
1 1 1 good
2 2 4 fair
3 4 5  bad