On 23/07/2018 3:03 PM, Hadley Wickham wrote:
Hi all,
Would you generally consider NULL to be a vector?
According to the language definition (in the doc directory), it is not:
"Vectors can be thought of as contiguous cells containing data. Cells
are accessed through indexing operations such as x[5]. More details are
given in Indexing.
R has six basic (‘atomic’) vector types: logical, integer, real,
complex, string (or character) and raw. The modes and storage modes for
the different vector types are listed in the following table."
and later
"There is a special object called NULL. It is used whenever there is a
need to indicate or specify that an object is absent. It should not be
confused with a vector or list of zero length."
Duncan Murdoch
Base R functions are
a little inconsistent:
## In favour
``` r
identical(as.vector(NULL), NULL)
#> [1] TRUE
identical(as(NULL, "vector"), NULL)
#> [1] TRUE
# supports key vector vector generics
length(NULL)
#> [1] 0
NULL[c(3, 4, 5)]
#> NULL
NULL[[1]]
#> NULL
```
## Against
``` r
is.vector(NULL)
#> [1] FALSE
is(NULL, "vector")
#> [1] FALSE
```
## Abstentions
``` r
is.atomic(NULL)
#> [1] TRUE
# documentation states "returns NULL if x is of an atomic type (or NULL)"
# is "or" exclusive or inclusive?
```
Hadley
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