group_by: Group by one or more variables
In privefl/bigdfr: Operate with Data Frames Stored on Disk

Group by one or more variables

## S3 method for class 'FDF'
ungroup(x, ...)

ungroup(x, ...)

## S3 method for class 'FDF'
group_by(.data, ..., add = FALSE)

group_by(.data, ..., add = FALSE)

`x`	A FDF.
`...`	Not used.
`.data`	A FDF.
`add`	When `add = FALSE`, the default, `group_by()` will override existing groups. To add to the existing groups, use `add = TRUE`.

(test <- FDF(datasets::iris))
(test2 <- group_by(test, Species))
test2$groups
group_by(test, starts_with("Sepal"))$groups
group_by(test2, Sepal.Length, add = TRUE)$groups