Variable (covariate) names with dashes are not parsed about formulaic HOT 4 CLOSED

Hi!

Thanks for writing in to report the issue. Just like in a Python expression, - has special meaning and cannot be used without some kind of quoting. For example, in python b-foo means b minus foo. In a formula it means b set difference foo.

If you want to use the column b-foo, then just quote the column name. You can do this using back-ticks.

import pandas
from formulaic import model_matrix

df = pandas.DataFrame({
    'y': [0, 1, 2],
    'a': ['A', 'B', 'C'],
    'b-foo': [0.3, 0.1, 0.2],
})

y, X = model_matrix("y ~ a + `b-foo`", df)

This outputs the desired module matrix :).

You can learn more about the formula grammar here.

from formulaic.

It is there (see third row in table within screenshot below):

But perhaps not called out as much as it should be. The documentation will definitely be enriched in the future with how-to guides/etc once I find some time!

from formulaic.

Thanks, this answers my question and resolves the issue. Did I miss it, or does the documentation not include this info?

from formulaic.

Thanks for helping me find that in the documentation! The table format is helpful.

from formulaic.