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

I think I may have solved the problem. I believe it is due to NA value in the data. Because after I removed the na using say

x<-na.omit(original_data)

then apply the levene test on x, the warning message disappears.

Hopefully this is the cause of the problem.