dots {base} | R Documentation |
..1
, etc used in Functions...
and ..1
, ..2
etc are used to refer to
arguments passed down from a calling function. These (and the
following) can only be used inside a function which has
...
among it formal arguments.
...elt(n)
is a functional way to get ..<n>
and
basically the same as eval(paste0("..", n))
, just more elegant
and efficient.
Note that switch(n, ...)
is very close, differing by returning
NULL
invisibly instead of an error when n
is zero or
too large.
...length()
returns the number of expressions in ...
.
This is the same as length(list(...))
but without evaluating
the expressions in ...
(which happens with list(...)
).
...length() ...elt(n)
n |
a positive integer, not larger than the number of expressions
in ..., which is the same as |
...
and ..1
, ..2
are reserved words in
R, see Reserved
.
For more, see the Introduction to R manual for usage of these syntactic elements, and dotsMethods for their use in formal (S4) methods.
tst <- function(n, ...) ...elt(n) tst(1, pi=pi*0:1, 2:4) ## [1] 0.000000 3.141593 tst(2, pi=pi*0:1, 2:4) ## [1] 2 3 4 try(tst(1)) # -> Error about '...' not containing an element. tst.dl <- function(x, ...) ...length() tst.dl(1:10) # 0 (because the first argument is 'x') tst.dl(4, 5) # 1 tst.dl(4, 5, 6) # 2 namely '5, 6' tst.dl(4, 5, 6, 7, sin(1:10), "foo"/"bar") # 5. Note: no evaluation!