[R] subsetting by NA

[Spencer Graves]

      Have you considered "is.na"? 

      My favorite tool for answering questions like this is 
www.r-project.org -> search -> "R site search".  When I asked there for 
"subsetting by NA" just now, I got 101 hits, the third of which 
mentioned "is.na".  Also, the posting guide 
"R-project.org/posting-guide.html" gives other useful tips for how to 
find information about R. 

      hope this helps.  spencer graves

Benjamin M. Osborne wrote:

>I want to know where all the NAs are in a matrix.  The data frame looks like
>this:
>
>  
>
>>vmc[1:5,]
>>    
>>
>       date year month day snow.new prcp      tmin snow.dep       tmax
>1 01NOV1954 1954    11   1       NA   NA -14.44444       NA 12.2222222
>2 02NOV1954 1954    11   2       NA   NA -13.88889       NA  2.2222222
>3 03NOV1954 1954    11   3       NA   NA -16.66667       NA -1.1111111
>4 04NOV1954 1954    11   4       NA   NA        NA       NA -0.5555556
>5 05NOV1954 1954    11   5       NA   NA -17.22222       NA -2.7777778
>       tmean yearmo
>1  -1.111111 195411
>2  -5.833333 195411
>3  -8.888889 195411
>4         NA 195411
>5 -10.000000 195411
>  
>
>
>This does not work:
>  
>
>>subset(vmc, snow.new==NA)
>>    
>>
> [1] date     year     month    day      snow.new prcp     tmin     snow.dep
> [9] tmax     tmean    yearmo
><0 rows> (or 0-length row.names)
>
>
>Because:
>  
>
>>NA==NA
>>    
>>
>[1] NA
>
>How can I return all rows of this data frame that contain NA in a particular
>field?
>
>Thanks,
>Ben Osborne
>
>  
>