Is it possible to use a popup menu to select columns in a matrix and then apply a function to the selected column?

Hello,

Need to apply my own boundary conditions to different parts of a geometry from the decomosed matrix, dl. Can I select the column which I need to use from a popup menu and use the selected column to apply boundary conditions on my own nodes which are to be entered in an edit text box? Can the entries in the pop up menu be numbered corresponding to each column in the matrix? A fumction will handle selecting the nodes but how will I get the function to know row to work on?

Thanks, Brian