[Rd] possible bug: NULL equality in lists.
Uwe Ligges
ligges at statistik.uni-dortmund.de
Tue Mar 7 16:13:02 CET 2006
Charles Dupont wrote:
> I was messing around with R and I found an example R behaving oddly:
>
> a <- alist(NULL, "bob", c(3,6,2,3))
> a
> a == 'NULL'
> a == "NULL"
> a == 'cat'
>
Always use is.null() to test on NULL, as in:
sapply(a, is.null)
Uwe Ligges
> If I create a list with a NULL value
> >a <- alist(NULL, "bob", c(3,6,2,3))
> >a
> [[1]]
> NULL
>
> [[2]]
> [1] "bob"
>
> [[3]]
> c(3, 6, 2, 3)
>
> and run some tests on 'a', the '== "NULL' test returns TRUE for the NULL
> entry in the list 'a'.
> >a == 'NULL'
> [1] TRUE FALSE FALSE
> >a == "NULL"
> [1] TRUE FALSE FALSE
> >a == 'cat'
> [1] FALSE FALSE FALSE
>
> This is consistent for every example of NULL's in a list that I can
> think of.
>
> Is this a bug or undocumented correct behavior?
>
> Here is my version output
>
> platform i486-pc-linux-gnu
> arch i486
> os linux-gnu
> system i486, linux-gnu
> status
> major 2
> minor 2.0
> year 2005
> month 10
> day 06
> svn rev 35749
> language R
>
>
> Thanks
>
> Charles
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