gapply function

Apply a Function by Groups

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

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

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 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.

Returns

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

References

Pinheiro, J.C., and Bates, D.M. (2000) "Mixed-Effects Models in S and S-PLUS", Springer, esp. sec. 3.4.

Author(s)

José Pinheiro and Douglas Bates bates@stat.wisc.edu

See Also

gsummary

Examples

## Find number of non-missing "conc" observations for each Subject
gapply( Phenobarb, FUN = function(x) sum(!is.na(x$conc)) )

# Pinheiro and Bates, p. 127 
table( gapply(Quinidine, "conc", function(x) sum(!is.na(x))) )
changeRecords <- gapply( Quinidine, FUN = function(frm)
    any(is.na(frm[["conc"]]) & is.na(frm[["dose"]])) )