margin.vars: Margin variables
Description
Works out list of variables to margin over to get desired margins.
Usage
margin.vars(vars = list(NULL, NULL), margins = NULL)
Author
Hadley Wickham <h.wickham@gmail.com>
Arguments
- vars
- list of column and row variables 
- margins
- vector of variable names to margin over 
Details
Variables that can't be margined over are dropped silently.