Sometimes there can be terms in a formula that refer to a matrix instead of a single predictor. Because we can handle search_terms of predictors, this function breaks the matrix term into individual predictors to handle separately, as that is probably the intention of the user.
break_up_matrix_term(formula, data)
A formula for a valid model.
The original data frame with a matrix as predictor.
a list containing the expanded formula and the expanded data frame.