rapply {base}

R Documentation

Recursively Apply a Function to a List

Description

rapply is a recursive version of lapply.

Usage

rapply(object, f, classes = "ANY", deflt = NULL,
       how = c("unlist", "replace", "list"), ...)

Arguments

object	A list.
f	A function of a single argument.
classes	A character vector of class names, or "ANY" to match any class.
deflt	The default result (not used if how = "replace").
how	A character string matching the three possibilities given: see ‘Details’.
...	additional arguments passed to the call to f.

Details

This function has two basic modes. If how = "replace", each element of the list which is not itself a list and has a class included in classes is replaced by the result of applying f to the element.

If the mode is how = "list" or how = "unlist", the list is copied, all non-list elements which have a class included in classes are replaced by the result of applying f to the element and all others are replaced by deflt. Finally, if how = "unlist", unlist(recursive = TRUE) is called on the result.

The semantics differ in detail from lapply: in particular the arguments are evaluated before calling the C code.

Value

If how = "unlist", a vector, otherwise a list of similar structure to object.

References

Chambers, J. A. (1998) Programming with Data. Springer.
(rapply is only described briefly there.)

See Also

lapply, dendrapply.

Examples

X <- list(list(a=pi, b=list(c=1:1)), d="a test")
rapply(X, function(x) x, how="replace")
rapply(X, sqrt, classes="numeric", how="replace")
rapply(X, nchar, classes="character",
       deflt = as.integer(NA), how="list")
rapply(X, nchar, classes="character",
       deflt = as.integer(NA), how="unlist")
rapply(X, nchar, classes="character", how="unlist")
rapply(X, log, classes="numeric", how="replace", base=2)

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