[Rd] possible bug: NULL equality in lists.
Seth Falcon
sfalcon at fhcrc.org
Tue Mar 7 16:37:12 CET 2006
Uwe Ligges <ligges at statistik.uni-dortmund.de> writes:
> 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:
What should I do if I want to check for the string "NULL"?
> a <- list(NULL, "NULL", NA, "NA")
> a == "NULL"
[1] TRUE TRUE FALSE FALSE
> a == "NA"
[1] FALSE FALSE TRUE TRUE
These are because of as.character:
> as.character(a)
[1] "NULL" "NULL" "NA" "NA"
Yet,
> as.character(NULL)
character(0)
> as.character(NA)
[1] NA
+ seth
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