ENmisc (version 1.2-7)

mtapply: Apply a Function of Multiple Arguments Over a Ragged Array

Description

Apply a function of multiple arguments to cells of a identically structures ragged arrays, that is to each set of (non-empty) groups of values given by a unique combination of the levels of certain factors. It is a hybrid of tapply and mapply.

Usage

mtapply(X, INDEX, FUN = NULL, simplify = TRUE)

Arguments

X

a list of atomic objects, typically vectors, all of the same length

INDEX

list of factors, each of same length as X. The elements are coerced to factors by as.factor.

FUN

the function to be applied, or NULL. In the case of functions like +, %*%, etc., the function name must be backquoted or quoted. If FUN is NULL, tapply returns a vector which can be used to subscript the multi-way array mtapply normally produces.

simplify

If FALSE, tapply always returns an array of mode "list". If TRUE (the default), then if FUN always returns a scalar, tapply returns an array with the mode of the scalar.

Value

If FUN is not NULL, it is passed to match.fun, and hence it can be a function or a symbol or character string naming a function.

When FUN is present, mtapply calls FUN for each set of cells that has any data in it. If FUN returns a single atomic value for each such cell (e.g., functions mean or var) and when simplify is TRUE, tapply returns a multi-way array containing the values, and NA for the empty cells. The array has the same number of dimensions as INDEX has components; the number of levels in a dimension is the number of levels (nlevels()) in the corresponding component of INDEX. Note that if the return value has a class (e.g. an object of class "Date") the class is discarded.

If FUN does not return a single atomic value, tapply returns an array of mode list whose components are the values of the individual calls to FUN, i.e., the result is a list with a dim attribute.

When there is an array answer, its dimnames are named by the names of INDEX and are based on the levels of the grouping factors (possibly after coercion).

For a list result, the elements corresponding to empty cells are NULL.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

the functions link{tapply}, mapply, by and aggregate (using tapply); apply, lapply with its versions sapply and mapply.

Examples

# NOT RUN {
require(Hmisc)
x<-1:10
fc<-rep(c("a","b"),each=5)
wt<-1:10
mtapply(list(x,wt),fc,wtd.mean)
mtapply(list(x,rep(1/10,10)),fc,wtd.mean)
# }