向量因子水平的指标

Question

How to get vector containing indices of each element in the level attribute of the vector k? That is how to get vector (1, 2, 1) for the k ?

 k <- factor(c('a', 'b', 'a'))
> k
[1] a b a
Levels: a b

Answer 1

We can use match

match(k, levels(k))
#[1] 1 2 1

Or convert to numeric to get the integer storage values

as.integer(k)
[1] 1 2 1