// discrete scales change the dtype
// from category to int. Use a new dataframe
// to collect these results.
df = pd.DataFrame({}, index=range(len(data)))
cat_cols = []
// Loop through each variable, mapping across each scale,
// then joining back into the copy of the data
After Change
// from category to int. Use a new dataframe
// to collect these results.
// Using `type` preserves the subclass of pd.DataFrame
df = type(data)(index=data.index)
cat_cols = []
// Loop through each variable, mapping across each scale,
// then joining back into the copy of the data
