On Mon, Apr 25, 2011 at 12:53:40PM -0700, Lisa wrote:
> Dear All,
>
> I just want to remove “NA” from the levels of a factor. For example:
>
> d<-data.frame(matrix(c("ww","ww","xx","yy","ww","yy","xx","yy","NA"),
> ncol=3, byrow=TRUE))
>
> > factor(d[, 3], exclude=NA)
> [1] xx yy NA
> Levels: NA xx yy
>
> But “NA” is still listed in the levels. How can I solve this problem?
The column d[, 3] is already a factor. It is possible to avoid
this using
d<-data.frame(matrix(c("ww","ww","xx","yy","ww","yy","xx","yy","NA"),
ncol=3, byrow=TRUE), stringsAsFactors=FALSE)
Then, we get
factor(d[, 3], exclude="NA")
[1] xx yy <NA>
Levels: xx yy
Hope this helps.
Petr Savicky.
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