grouped_ffdf: A grouped ffdf.
In edwindj/ffbase2: Dplyr for 'ff'

The easiest way to create a grouped ffdf is to call the group_by method on a ffdf or data source: this will take care of capturing the unevalated expressions for you.

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grouped_ffdf(data, vars, is_sorted = FALSE)

is.grouped_ffdf(x)

`data`	a data source or data frame.
`vars`	a list of quoted variables.
`is_sorted`	if `data` is sorted on `vars` is_sorted should be set to `TRUE` to avoid unnecesary sorting
`x`	an object to check