Pass column name to lpSolve obj from drop down

Question

Pass column name to lpSolve obj from drop down.

OptTotal total is a column name for optimisation, I would like a drop down box to select which column to optimise against but can not figure it out.

  obj <- rv$products$OptTotal

I would like something like the below

obj <- rv$products$get(Input$ColumnName) This does not work but explains what I would like.