[R] substituting level for NA in factor column

Bert Gunter gunter.berton at gene.com
Tue Jan 18 23:54:29 CET 2011

Well, (have you read "An Intro to R," which I think might have enabled
you to figure this out for yourself?)....

Convert the factor to character, use is.na() to substitute, convert
back to factor. e.g.

> z <- factor (c(1,2,3,NA))
>  z<- as.character(z)
> z[is.na(z)] <- "U"
> factor(z)
[1] 1 2 3 U
Levels: 1 2 3 U

HOWEVER, this is almost certainly a BAD IDEA, as you have now
essentially lost the ordering of the levels, which is important
information for modeling. In general, R handles NA's (perhaps not
always gracefully) and you should leave them as such and let R do its
job. A lot of effort by wise folks has been expended to make this


On Tue, Jan 18, 2011 at 2:25 PM,  <Kurt_Helf at nps.gov> wrote:
> Greetings
>     I have a bunch of NAs in a column of categorical variables designating
> the size classes (e.g., smallest to largest: 1,2,3,4) of cave crickets.
> I'd like to substitute "U" (for unknown) for the NAs.  Can anyone give me
> an idea how to do this?  Thanks in advance.
> Cheers
> Kurt
> ***************************************************************
> Kurt Lewis Helf, Ph.D.
> Ecologist
> EEO Counselor
> National Park Service
> Cumberland Piedmont Network
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> Cumberland Piedmont Network (CUPN) Homepage:
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Bert Gunter
Genentech Nonclinical Biostatistics

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