[R] Subassignments involving NAs in data frames

[Thomas Lumley]

On Thu, 9 Jun 2005, McGehee, Robert wrote:

> I'm seeing some inconsistent behavior when re-assigning values in a data
> frame. The first assignment turns all of the 0s in my data frame to 2s,
> the second fails to do so.
>
>> df1 <- data.frame(a = c(NA, 0, 3, 4))
>> df2 <- data.frame(a = c(NA, 0, 0, 4))
>> df1[df1 == 0] <- 2 ## Works
>> df2[df2 == 0] <- 2
> Error: NAs are not allowed in subscripted assignments

Hmm. This looks like a bug to me.

> Checking an old news file I see this:
>    o	Subassignments involving NAs and with a replacement value of
> 	length > 1 are now disallowed.	(They were handled
> 	inconsistently in R < 2.0.0, see PR#7210.)  For data frames
> 	they are disallowed altogether, even for logical matrix indices
> 	(the only case which used to work).
>
> which leaves me to believe that the assignment for both df1 and df2
> should fail ("data frame ... disallowed altogether"), however that seems
> not to be the case, since the example works for df1.

Yes, I think the bug is that it works

> Also, the
> vectorized version works as expected (because the replacement value has
> a length of 1).
>
>> vec1 <- c(NA, 0, 3, 4)
>> vec2 <- c(NA, 0, 0, 4)
>> vec1[vec1 == 0] <- 2 ## Works
>> vec2[vec2 == 0] <- 2 ## Also works

I'm not sure that this is supposed to work, either, but it might be.

> Is this behavior for data frames intentional? What's the best
> alternative to df1[df1 == 0] <- 2 that doesn't fail in situations such
> as df2? A simple loop over columns?

df2[df2 %in% 0] is the recommended method.

 	-thomas