R: The Names of an Object

names {base} | R Documentation

## The Names of an Object

### Description

Functions to get or set the names of an object.

### Usage

    names(x)
    names(x) <- value

### Arguments

`x` | an R object.
`value` | a character vector of up to the same length as `x`, or `NULL`.

### Details

`names` is a generic accessor function, and `names<-` is a generic replacement function. The default methods get and set the `"names"` attribute of a vector (including a list) or pairlist.

For an `environment` `env`, `names(env)` gives the names of the corresponding list, i.e., `names(as.list(env, all.names = TRUE))` which are also given by `ls(env, all.names = TRUE, sorted = FALSE)`. If the environment is used as a hash table, `names(env)` are its “keys”.

If `value` is shorter than `x`, it is extended by character `NA`s to the length of `x`.

It is possible to update just part of the names attribute via the general rules: see the examples. This works because the expression there is evaluated as `z <- "names<-"(z, "[<-"(names(z), 3, "c2"))`.

The name `""` is special: it is used to indicate that there is no name associated with an element of a (atomic or generic) vector. Subscripting by `""` will match nothing (not even elements which have no name).

A name can be character `NA`, but such a name will never be matched and is likely to lead to confusion.

Both are primitive functions.

### Value

For `names`, `NULL` or a character vector of the same length as `x`. (`NULL` is given if the object has no names, including for objects of types which cannot have names.) For an environment, the length is the number of objects in the environment but the order of the names is arbitrary.

For `names<-`, the updated object. (Note that the value of `names(x) <- value` is that of the assignment, `value`, not the return value from the left-hand side.)

### Note

For vectors, the names are one of the attributes with restrictions on the possible values. For pairlists, the names are the tags and converted to and from a character vector.

For a one-dimensional array the `names` attribute really is `dimnames[[1]]`.

Formally classed aka “S4” objects typically have `slotNames()` (and no `names()`).

### References

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

### See Also

`slotNames`, `dimnames`.

### Examples

    # print the names attribute of the islands data set
    names(islands)

    # remove the names attribute
    names(islands) <- NULL
    islands
    rm(islands) # remove the copy made

    z <- list(a = 1, b = "c", c = 1:3)
    names(z)
    # change just the name of the third element.
    names(z)[3] <- "c2"
    z

    z <- 1:3
    names(z)
    ## assign just one name
    names(z)[2] <- "b"
    z

[Package base version 3.5.1 Index]