# is.null.DN: Are the Dimnames 'dn' NULL-like ? In Matrix: Sparse and Dense Matrix Classes and Methods

## Description

Are the `dimnames` `dn` `NULL`-like?

`is.null.DN(dn)` is less strict than `is.null(dn)`, because it is also true (`TRUE`) when the dimnames `dn` are “like” `NULL`, or `list(NULL,NULL)`, as they can easily be for the traditional R matrices (`matrix`) which have no formal `class` definition, and hence much freedom in how their `dimnames` look like.

## Usage

 `1` ``` is.null.DN(dn) ```

## Arguments

 `dn` `dimnames()` of a `matrix`-like R object.

## Value

`logical` `TRUE` or `FALSE`.

## Note

This function is really to be used on “traditional” matrices rather than those inheriting from `Matrix`, as the latter will always have dimnames `list(NULL,NULL)` exactly, in such a case.

## Author(s)

Martin Maechler

`is.null`, `dimnames`, `matrix`.
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14``` ```m <- matrix(round(100 * rnorm(6)), 2,3); m1 <- m2 <- m3 <- m4 <- m dimnames(m1) <- list(NULL, NULL) dimnames(m2) <- list(NULL, character()) dimnames(m3) <- rev(dimnames(m2)) dimnames(m4) <- rep(list(character()),2) m4 ## prints absolutely identically to m stopifnot(m == m1, m1 == m2, m2 == m3, m3 == m4, identical(capture.output(m) -> cm, capture.output(m1)), identical(cm, capture.output(m2)), identical(cm, capture.output(m3)), identical(cm, capture.output(m4))) ```