rapply | R Documentation |
rapply
is a recursive version of lapply
with
flexibility in how the result is structured (how = ".."
).
rapply(object, f, classes = "ANY", deflt = NULL, how = c("unlist", "replace", "list"), ...)
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 |
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.
If how = "unlist"
, a vector, otherwise “list-like”
of similar structure as object
.
Chambers, J. A. (1998)
Programming with Data.
Springer.
(rapply
is only described briefly there.)
lapply
, dendrapply
.
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")) })
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