jcfisher

When using a [tibble](https://tibble.tidyverse.org/), `att` fails with the error `Error in `[.data.frame`(TEi, idt) : undefined columns selected`. This is occurring because of line 374 (using the GitHub formatting), `TEi

When you create a `cem` object using a factor variable as a treatment, attempting to use `att` to run a logistic regression on that object fails. It looks like this...