object
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an object to which the function will be applied - usually
a groupedData object or a data.frame .
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FUN
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function to apply to the distinct sets of rows
of the data frame object defined by the values of
groups .
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form
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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
formula(object) .
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level
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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.
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groups
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an optional factor that will be used to split the
rows into groups. Defaults to getGroups(object, form, level) .
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...
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optional additional arguments to the summary function
FUN . Often it is helpful to specify na.rm = TRUE .
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