[R] missing -> nonmissing levels

[Chuck Cleland]

Jon Minton wrote:
> Hi, 
> 
> I expect this is simple but haven’t found an answer looking on the
> archives...
> 
> I want to convert ‘NA’ (missing) to particular levels (nonmissing) in factor
> vectors.
> 
> e.g. I know
> 
>> X <- c(1, 2, 3)
> 
>> summary(X)
> 
>    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
> 
>     1.0     1.5     2.0     2.0     2.5     3.0 
> 
>> X <- as.factor(X)
> 
>> summary(X)
> 
> 1 2 3 
> 
> 1 1 1 
> 
>> levels(X)
> 
> [1] "1" "2" "3"
> 
>> levels(X) <- c("A", NA, "B")
> 
>> summary(X)
> 
>    A    B NA's 
> 
>    1    1    1
> 
> But what if I want to turn the NA back into a level? 
> 
> How do I do this?

  One way is to use recode() in the car package by John Fox.  For example:

library(car)

X <- factor(c(1, NA, 3))

X
[1] 1    <NA> 3
Levels: 1 3

recode(X, "NA='J'")
[1] 1 J 3
Levels: 1 3 J

> Thanks,  Jon
> 
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-- 
Chuck Cleland, Ph.D.
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