[R] NA's in if statement

[Spencer Graves]

      The following provides a sample use if "is.na" in an context 
similar to yours, that also uses vector arithmetic, so you don't need a 
loop: 

 > tst <- (-2):2
 > (tst2 <- 1+tst/(tst^2))
[1] 0.5 0.0 NaN 2.0 1.5
 > (sel <- (tst2==0))
[1] FALSE  TRUE    NA FALSE FALSE
 > sel[is.na(tst2)] <- FALSE
 > tst2[sel] <- 123
 > tst2
[1]   0.5 123.0   NaN   2.0   1.5

      hope this helps.  spencer graves

michael watson (IAH-C) wrote:

>Some careful use of is.na() may help.
>Either by using it to remove NA values or as part of the if statement.
> 
>Or:
> 
>my.wdir <- na.omit(dat$wdir)
>for(i in 1:length(my.wdir)) {
> 
>#etc
>
>	-----Original Message----- 
>	From: r-help-bounces at stat.math.ethz.ch on behalf of lindsayv at unbc.ca 
>	Sent: Fri 2/11/2005 9:34 PM 
>	To: r-help at stat.math.ethz.ch 
>	Cc: 
>	Subject: [R] NA's in if statement
>	
>	
>
>	Hello,
>	
>	I am having trouble dealing with NA values in if statements such as:
>	i<-1
>	for(i in 1:length(dat$wdir)){
>	if (dat$wspd[i]==0){
>	dat$wdir[i]<-0
>	}
>	}
>	
>	I get the following error due to the presence of NS values in the data:
>	Error in if (dat$wspd[i] == 0) { : missing value where TRUE/FALSE needed
>	
>	Sorry if this is an old question but I was unable to resolve this from the
>	info on na.action etc. or old archives.
>	
>	Thank you for any suggestions,
>	
>	Vera Lindsay
>	
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