Weird add_constr_custom() behaviors

[christopherkenny]

• If a call to a function is present using ::, you get the following warning.

Error in `rlang::as_string()`:
! Can't convert a call to a string.

Workaround: Define the required function in the global environment before using it, like colMins <- matrixStats::colMins before declaring the custom constraint.

• Sub-redist_maps after filtering fail if you rely on the district number and the numbers are not sequential. On an example Iowa map, filter out district 2 and then try to subset to access district 2, causing a NaN issue.
  Workaround: renumber the existing_col when you create the map

[christopherkenny]

:: issue fixed by explicitly using a child environment. That's wrong, still broken.

[CoryMcCartan]

Can you elaborate on the 2nd issue?

Shouldn't accessing indices that don't exist cause problems?