Arguments
object
an object to which the function will be applied - usually
a groupedData object or a data.frame. Must inherit from
class data.frame.
which
an optional character or positive integer vector
specifying which columns of object should be used with
FUN. Defaults to all columns in object.
FUN
function to apply to the distinct sets of rows
of the data frame object defined by the values of
groups.
form
an optional one-sided formula that defines the groups.
When this formula is given the right-hand side is evaluated in
object, converted to a factor if necessary, and the unique
levels are used to define the groups. Defaults to
level
an optional positive integer giving the level of grouping
to be used in an object with multiple nested grouping levels.
Defaults to the highest or innermost level of grouping.
groups
an optional factor that will be used to split the
rows into groups. Defaults to getGroups(object, form, level).
...
optional additional arguments to the summary function
FUN. Often it is helpful to specify na.rm = TRUE.