base (version 3.3.2)

c: Combine Values into a Vector or List

Description

This is a generic function which combines its arguments. The default method combines its arguments to form a vector. All arguments are coerced to a common type which is the type of the returned value, and all attributes except names are removed.

Usage

## S3 Generic function
c(…)
# S3 method for default
c(…, recursive = FALSE, use.names = TRUE)

Arguments

…

objects to be concatenated.

recursive

logical. If recursive = TRUE, the function recursively descends through lists (and pairlists) combining all their elements into a vector.

use.names

logical indicating if names should be preserved.

Value

NULL or an expression or a vector of an appropriate mode. (With no arguments the value is NULL.)

S4 methods

This function is S4 generic, but with argument list (x, ..., recursive = FALSE).

Details

The output type is determined from the highest type of the components in the hierarchy NULL < raw < logical < integer < double < complex < character < list < expression. Pairlists are treated as lists, but non-vector components (such names and calls) are treated as one-element lists which cannot be unlisted even if recursive = TRUE. Note that factors are treated only via their internal integer codes; one proposal has been to use

   c.factor <- function(..., recursive=TRUE) unlist(list(...), recursive=recursive)

if factor concatenation by c() should give a factor. c is sometimes used for its side effect of removing attributes except names, for example to turn an array into a vector. as.vector is a more intuitive way to do this, but also drops names. Note too that methods other than the default are not required to do this (and they will almost certainly preserve a class attribute). This is a primitive function.

References

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

See Also

unlist and as.vector to produce attribute-free vectors.

Examples

c(1,7:9)
c(1:5, 10.5, "next")

## uses with a single argument to drop attributes
x <- 1:4
names(x) <- letters[1:4]
x
c(x)          # has names
as.vector(x)  # no names
dim(x) <- c(2,2)
x
c(x)
as.vector(x)

## append to a list:
ll <- list(A = 1, c = "C")
## do *not* use
c(ll, d = 1:3) # which is == c(ll, as.list(c(d = 1:3))
## but rather
c(ll, d = list(1:3))  # c() combining two lists

c(list(A = c(B = 1)), recursive = TRUE)

c(options(), recursive = TRUE)
c(list(A = c(B = 1, C = 2), B = c(E = 7)), recursive = TRUE)