[R] Levels of a factor

David Winsemius dwinsemius at comcast.net
Wed Jul 24 20:47:57 CEST 2013

On Jul 24, 2013, at 11:35 AM, David Winsemius wrote:

> On Jul 24, 2013, at 6:25 AM, Borja Rivier wrote:
>> Hi all,
>> I am having a bit of trouble using the levels() function.
>> I have a factor with many elements, and when I use the function levels() to
>> extract the list of unique elements, some of the elements returned are not
>> actually in the factor.
>> snipped
> When you take a subset of a factor vector, the levels are not reduced to the unique values in the new vector. There is droplevels function that would need to be applied if you already have such a vector, and there is a drop argument that you need to set to TRUE in the `[.factors`

Make that `[.factor`

> call if you want to "attack the problem at the source".
> ?`[.factor  # missing trailing back-tick


> ?droplevels
> -- 

David Winsemius
Alameda, CA, USA

More information about the R-help mailing list