ompr 0.8.1

General changes

You can now assign coefficients to all column/row combinations using colwise in the experimental MILPModel backend.
Non-existent indexes in sum_expr now produce a warning instead of an error. The missing indexes will be ignored (#202).

Fixed a bug were get_solution could return mixed up values when variables had partially similar names (eg: s[i] and bus[i]) by @hugolarzabal (#244).
Fixed a bug on where an if-condition had an input with length != 1.
Fixed some minor issues with newer data.table versions

Removed dplyr dependency
Added MILPModel, a new, vectorized backend for mixed integer linear programs that can handle very large models. It will eventually replace MIPModel.
Added two functions (get_column_duals, get_row_duals) to extract the dual (column and row) values from an LP.
The minimum supported R version is now 3.2.0
get_solution now always return a solution, even if the solution status is not optimal.
get_solution has a third argument type with permitted values being “primal” and “dual” to return the respective column primal or dual values.

ompr now uses sparse constraint matrices. extract_constraints now returns a sparse matrix and objective_function returns a sparse vector.
The minimum supported R version is now 3.3.0
Fixed an issue with Rcpp. The minimum Rcpp version is now 0.12.12