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, ...).

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, whereas 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 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.

Examples

Run this code

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)

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