[R] functions for special na handling?

[Sundar Dorai-Raj]

Sundar Dorai-Raj wrote:

> 
> 
> Robert Sams wrote:
> 
>> hi,
>>
>> i need a function that can replace na's in univariate ts objects with 
>> a value interpolated linearly using the adjacent non-na values. for 
>> example, the function i need (myfun) would do the following
>>
>>
>>> x <- ts(10,11.4,NA,12,9.7)
>>> y <- myfun(x)
>>> y
>>
>>
>> 10 11.4 11.7 12 9.7
>>
>> i can code an na.action method myself to accomplish this, but has 
>> someone else already coded routines of this nature?
>>
>> many thanks,
>> robert
>>
>>
>> Robert Sams
> 
> 
> Hi Robert,
>   Will the following do?
> 
> na.approx <- function(x) {
>   na <- is.na(x)
>   if(all(!na)) return(x)
>   i <- seq(along = x)
>   x[na] <- approx(i[!na], x[!na], i[na])$y
>   x
> }
> 
>  > x <- c(10,11.4,NA,12,9.7)
>  > na.approx(x)
> [1] 10.0 11.4 11.7 12.0  9.7
> 
> 

One other note: na.approx as written above will return NA if the first 
or last element of your vector is missing. See ?approx on how to change 
this behaviour.

--sundar