[R] If else in R code

[Peter Dalgaard]

Simon Blomberg wrote:
> How about:
>
> a<-c("2001-02-1",NA,NA)
> b<-c("2001-03-1","2001-03-2","2001-03-3")
>
>  res <- ifelse(is.na(a), as.character(as.Date(b)-2),
> as.character(as.Date(a)))
> res
>
> Or with no ifelse:
>
>  res <- a
>  res[is.na(a)] <- as.character(as.Date(b[is.na(a)])-2)
>  res
>
>   
What's up with the as.character stuff?

 res <- a
 res[is.na(res)] <- b[is.na(res)]-2

with ifelse, you have the annoyance that it strips attributes, so you 
need something like

 res <- ifelse(is.na(a),b-2, a)
 class(res) <- "Date"
 res




> Cheers,
>
> Simon.
>
> On Fri, 2008-02-08 at 14:23 +1300, Andrew McFadden wrote:
>   
>> Hi There 
>>
>> I am a new user of "R" and having a few problems
>>
>> a<-c("2001-02-1","NA","NA")
>> a<-as.Date(a,format = "%Y-%m-%d")
>>
>> b<-c("2001-03-1","2001-03-2","2001-03-3")
>> b<-as.Date(b,format = "%Y-%m-%d")
>>
>> c<-data.frame(a,b)
>>
>> I would like to write an if statement where if "a" is not null return
>> "a", if "a" is null (NA) return "b" less two days. Could someone help?.
>>
>>
>> Andrew  
>>
>>
>>
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