# Re: [R] use of NA's

From: Kjetil Brinchmann Halvorsen <kjetil_at_acelerate.com>
Date: Sat 06 Aug 2005 - 09:26:30 EST

Robert Kinley wrote:

>with NAs it's always safest to use the construction
>
>if(is.na(foo))
>
>rather than
>
>if(foo==NA)
>
>cheers Bob Kinley
>
>
>
>
And if it is not clear why, try:

> NA == NA
[1] NA
>
Kjetil

>Sent by: r-help-bounces@stat.math.ethz.ch
>05/08/2005 12:30
>
>To
>r-help@stat.math.ethz.ch
>cc
>
>Subject
>[R] use of NA's
>
>
>
>
>
>
>Can someone please explain why this works:
>
>
>
>>>d<-c(0,2,3,2,0,3,4,0,0,0,0,0)
>>>d.mat<-matrix(data=d,nrow=4,ncol=3,byrow=TRUE)
>>>for(i in 1:length(d.mat[1,])){
>>>
>>>
>>+ d.mat[,i][d.mat[,i]==0]<-mean(d.mat[,i][d.mat[,i]>0])
>>+ }
>>
>>
>
>Whereas:
>
>
>
>>d<-c(0,2,3,2,0,3,4,0,0,0,0,0)
>>d.mat<-matrix(data=d,nrow=4,ncol=3,byrow=TRUE)
>>d.mat[d.mat==0]<-NA
>>for(i in 1:length(d.mat[1,])){
>>
>>
>+ d.mat[,i][d.mat[,i]==NA]<-mean(d.mat[,i],na.rm=TRUE)
>+ }
>dosnt
>
>Thanks
>Tom
>
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```--

Kjetil Halvorsen.

Peace is the most effective weapon of mass construction.
--  Mahdi Elmandjra

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