| rapply {base} | R Documentation |
Recursively Apply a Function to a List
Description
rapply is a recursive version of lapply with
flexibility in how the result is structured (how = "..").
Usage
rapply(object, f, classes = "ANY", deflt = NULL,
how = c("unlist", "replace", "list"), ...)
Arguments
object |
a |
f |
a |
classes |
character vector of |
deflt |
the default result (not used if |
how |
character string partially matching the three possibilities given: see ‘Details’. |
... |
additional arguments passed to the call to |
Details
This function has two basic modes. If how = "replace", each
element of object which is not itself list-like and has a class
included in classes is replaced by the result of applying
f to the element.
Otherwise, with mode how = "list" or how = "unlist",
conceptually object
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.
In R 3.5.x and earlier, object was required to be a list,
which was not the case for its list-like components.
Value
If how = "unlist", a vector, otherwise “list-like”
of similar structure as object.
References
Chambers, J. A. (1998)
Programming with Data.
Springer.
(rapply is only described briefly there.)
See Also
Examples
X <- list(list(a = pi, b = list(c = 1L)), d = "a test")
# the "identity operation":
rapply(X, function(x) x, how = "replace") -> X.; stopifnot(identical(X, X.))
rapply(X, sqrt, classes = "numeric", how = "replace")
rapply(X, deparse, control = "all") # passing extras. argument of deparse()
rapply(X, nchar, classes = "character", deflt = NA_integer_, how = "list")
rapply(X, nchar, classes = "character", deflt = NA_integer_, how = "unlist")
rapply(X, nchar, classes = "character", how = "unlist")
rapply(X, log, classes = "numeric", how = "replace", base = 2)
## with expression() / list():
E <- expression(list(a = pi, b = expression(c = C1 * C2)), d = "a test")
LE <- list(expression(a = pi, b = expression(c = C1 * C2)), d = "a test")
rapply(E, nchar, how="replace") # "expression(c = C1 * C2)" are 23 chars
rapply(E, nchar, classes = "character", deflt = NA_integer_, how = "unlist")
rapply(LE, as.character) # a "pi" | b1 "expression" | b2 "C1 * C2" ..
rapply(LE, nchar) # (see above)
stopifnot(exprs = {
identical(E , rapply(E , identity, how = "replace"))
identical(LE, rapply(LE, identity, how = "replace"))
})