Contrasts can be applied only to factor

Question

I have a question about R.

I am using a test called levene.test to test a homogeneity of variance.

I know that you need a factor variable with at least two l

Answer 1

If your factor has only one level, you will get this error. To check to see the levels of your factor variables, use lapply(df, levels). It will return nothing for non-factor variables, but will easily let you identify which variable is the offender. This is especially helpful if, like me, you have hundreds of variables.