A Crunch Dataset "Grouped By" Something

Description

This is a subclass of crunch::CrunchDataset that has a field for recording "group_by" expressions.

Examples

## Not run: 
ds <- loadDataset("Your dataset name")
class(ds) ## "CrunchDataset"
grouped_ds <- group_by(ds, var1)
class(grouped_ds) ## "GroupedCrunchDataset"

## End(Not run)