Given the variables that form the rows and columns, and a set of desired
margins, works out which ones are possible. Variables that can't be
margined over are dropped silently.
Usage
margins(vars, margins = NULL)
Arguments
vars
a list of character vectors giving the variables in each
dimension
margins
a character vector of variable names to compute margins for.
TRUE will compute all possible margins.
Value
list of margining combinations, or NULL if none. These are
the combinations of variables that should have their values set to
(all)