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Converting Factors To Numbers In R

Sebastian Sauer shows us a pitfall of brute-force conversion of factors to integers:

Oh no! That’s not what we wanted! R has messed the thing up (?). The reason is that R sees the first factor level internally as the number 1 . The second level as number two. What’s the first factor level in our case? Let’s see:

factor(tips$sex) %>% head()#> [1] Female Male Male Male Female Male #> Levels: Female Malefactor(tips$sex_r) %>% head()#> [1] 1 0 0 0 1 0#> Levels: 0 1

That’s confusing: “0” is the first level of sex_r – internally for R represented by “1”. The second level of sex_r is “1” – internally represented by “2”.

Fortunately, we get the easy answer at the end of the post.