[R] Subsetting with missing data

[Ista Zahn]

It makes sense if you think it through.  Your index vector is

 a$y==0
 [1] FALSE  TRUE    NA FALSE  TRUE    NA    NA FALSE FALSE  TRUE

and ?"[" says

NAs in indexing:

     When extracting, a numerical, logical or character 'NA' index
     picks an unknown element and so returns 'NA' in the corresponding
     element of a logical, integer, numeric, complex or character
     result, and 'NULL' for a list.  (It returns '00' for a raw
     result.]

so this is what one has to expect. Here are a couple alternatives for
getting what you want.

a[which(a$y==0),]
a[a$y %in% 0,]

Best,
Ista

On Wed, Aug 15, 2012 at 4:06 PM, Robin Jeffries <rjeffries at ucla.edu> wrote:
> Simply put, I want to subset the data frame 'a' where 'y=0'.
>
>> a <- as.data.frame(cbind(x=1:10, y=c(1,0,NA,1,0,NA,NA,1,1,0)))
>> a
>     x  y
> 1   1  1
> 2   2  0
> 3   3 NA
> 4   4  1
> 5   5  0
> 6   6 NA
> 7   7 NA
> 8   8  1
> 9   9  1
> 10 10  0
>
>> names(a)
> [1] "x" "y"
>
>> table(a$y)
> 0 1
> 3 4
>
>> table(a$y, useNA="always")
>    0    1 <NA>
>    3    4    3
>
>> b <- a[a$y==0,]
>> b
>       x  y
> 2     2  0
> NA   NA NA
> 5     5  0
> NA.1 NA NA
> NA.2 NA NA
> 10   10  0
>
>> is(a$y)
> [1] "numeric" "vector"
>
>
> Instead of only pulling the rows where a$y==0, i'm getting where they're 0,
> OR NA. ? Again I feel like either something was changed when I wasn't
> looking.. or I'm reaaaaaaly forgetting something important.
>
> Thanks,
>
> Robin Jeffries
> MS, DrPH Candidate
> Department of Biostatistics,
> UCLA
> 530-633-STAT(7828)
> rjeffries at ucla.edu
>
>         [[alternative HTML version deleted]]
>
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