Apply a Function by Groups

Usage

gapply(object, FUN, form, level, groups, ...)

Arguments

object an object to which the function will be applied - usually a groupedData object or a data.frame.
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 formula(object).
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.

Description

Applies the function to the distinct sets of rows of the data frame defined by groups.

Value

Returns a data frame with as many rows as there are levels in the groups argument.

Author(s)

Jose Pinheiro and Douglas Bates

See Also

gsummary

Examples

library( lme )
data( Quinidine )
## Find number of non-missing "conc" observations for each Subject
gapply( Quinidine, function(x) sum(!is.na(x$conc)) )

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