Feature Request: step_ function for matrix indexing

[luisDVA]

Feature

This came up last week during the tidymodels workshop and Max suggest that I open an issue.

Sometimes a dataset contains a mix of qualitative character variables and dummy encoded variables. If we need to homogenize the data, a step_ function for this may be useful. Something that uses tidyselect for var selection and takes the name of the feature being described.

For example, going from this:

species	arboreal	terrestrial
sp a	0	1
sp b	1	0
sp c	1	0

to this:

species	locomotion
sp a	terrestrial
sp b	arboreal
sp c	arboreal

There are many ways to implement this, I have a silly write up here but a base approach would be better.

• if this already exists and I missed it because of unfamiliarity with ML terms please disregard

[EmilHvitfeldt]

I like it, it is basically a reverse step_dummy()