Extract Groups from a Data Frame

DESCRIPTION:

Each variable named in the expression after the `|' operator on the right hand side of form is evaluated in object. If more than one variable is indicated in level they are combined into a data frame; else the selected variable is returned as a vector. When multiple grouping levels are defined in form and `level > 1', the levels of the returned factor are obtained by pasting together the levels of the grouping factors of level greater or equal to level, to ensure their uniqueness.

USAGE:

getGroups(object, form, level) 

REQUIRED ARGUMENTS:

object
an object inheriting from class data.frame.

OPTIONAL ARGUMENTS:

form
an optional formula with a conditioning expression on its right hand side (i.e. an expression involving the `|' operator). Defaults to formula(object).
level
a positive integer vector with the level(s) of grouping to be used when multiple nested levels of grouping are present. Defaults to all levels of nesting.

VALUE:

either a data frame with columns given by the grouping factors indicated in level, from outer to inner, or, when a single level is requested, a factor representing the selected grouping factor.

SEE ALSO:

EXAMPLES:

getGroups(Pixel) 
getGroups(Pixel, level = 2)