HarlanH/JuliaData — pull request #41 by doobwa (2012-07-23 08:33:33+00:00)
Title: Formulas

I made a first pass at Issue #18. The main difference with the present code is a recursion on the left and right sides of the given `Expr`. Only `+`, `&`, and `*` are implemented (corresponding to feature unions, interaction terms, and both in the final ModelMatrix). If a column of the provided `DataFrame` is a `PooledDataVec`, then a matrix of indicators for each dummy variable is constructed, and the interaction terms are computed in turn.