Arguments
object
an object to be summarized - usually a data.frame
FUN
an optional summary function or a list of summary functions
to be applied to each variable in the frame. The function or
functions are applied only to variables in object
that vary
within the groups defined by groups
.
omitGroupingFactor
an optional logical value. When TRUE
the grouping factor itself will be omitted from the group-wise
summary but the levels of the grouping factor will continue to be
used as the row names for the data frame that is produced by the
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)
.
invariantsOnly
an optional logical value. When TRUE
only
those covariates that are invariant within each group will be
summarized. The summary value for the group is always the unique
value taken on by that covariate within the group. The colum
...
optional additional arguments to the summary functions
that are invoked on the variables by group. Often it is helpful to
specify na.rm = TRUE
.