Find groups in table data and apply functions to variables within groups.
This works like an SQL
"SELECT ... GROUP BY ..." statement.
groupvars (cellstr, numeric) is a list of the grouping variables, identified by name or index.
aggcalcs is a specification of the aggregate calculations to perform
on them, in the form
; ...}, where:
out_var (char) is the name of the output variable
fcn (function handle) is the function to apply to produce it
in_vars (cellstr) is a list of the input variables to pass to fcn
Returns a table.