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• a possible bug
• a question about package functionality
• a suggested code or documentation change, improvement to the code, or feature request

If you are reporting (1) a bug or (2) a question about code, please supply:

Right now package doesn't validate if features are factors. It leads to rather errors like this

## load package
library("cregg")

df <- tibble::tibble(
  choice = c(0, 1), f1 = c("a", "b"), f2 = c("d", "e"), id = c("1", "2")
)

mm(df, choice ~ f1 + f2, id = ~id)

## Error in fix.by(by.y, y) : 'by' must specify a uniquely valid column
## In addition: Warning messages:
## 1: Setting row names on a tibble is deprecated. 
## 2: Setting row names on a tibble is deprecated. 
## Called from: fix.by(by.y, y)

That's because make_term_levels_df blindly assumes that features are factors and ends up with a list of NULLs

lapply(df[c("f1", "f2")], levels)
## $f1
## NULL
## 
## $f2
## NULL

The problem affects at least amce, cj and mm.

A quick fix would be to simply test if that's the case:

if(!all(sapply(data[feature_names], is.factor))) stop("All features should be factors")

Alternatively one could attempt to fix the problem by explicitly casting to factors (maybe with a warning).