[R] removing factor values in the main data frame

[peter dalgaard]

> On 01 Mar 2016, at 18:33 , David L Carlson <dcarlson at tamu.edu> wrote:
> 
> You need to learn how to send emails in plain text since html gets mangled on r-help. See your message below. If I understand your question, it has to do with what happens to factor levels when you subset your data. Subsetting a factor does not remove empty factor levels. This is documented on the manual page for subset():
> 
> "Factors may have empty levels after subsetting; unused levels are not automatically removed. See droplevels for a way to drop all unused levels from a data frame."
> 

Also check ?"[.factor" and the drop=TRUE argument, which allows you to drop unused level from one particular factor. (Yes, there are good reasons that this is not the default.)

-pd 

> ------------------------------------
> David L Carlson
> Department of Anthropology
> Texas A&M University
> College Station, TX 77840-4352
> 
> 
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of hoda rahmati via R-help
> Sent: Tuesday, March 1, 2016 10:32 AM
> To: r-help at r-project.org
> Subject: [R] Fw: removing factor values in the main data frame
> 
> Hi all,I have the following main data frame:(mydata)        $ TE : num 40 40 20 20 20 20 20 20 20 40 ...        $ TR : num 49 49 28 28 28 28 28 28 28 49 ...        $ COUNTRY : Factor w/ 27 levels "","AU","BA","BE",..: 8 8 8 8 8 ...among the COUNTRY I just need US and AU,first I get a subset to contain just these two countries:        submydata=subset(mydata,COUNTRY%in%c("US","AU"))       factor(submydata$COUNTRY) but after this when I get str of mydata again I have the same data frame with no changes in COUNTRY, however I want mydata to be like: 
>        $ TE : num 40 40 20 20 20 20 20 20 20 40 ...        $ TR : num 49 49 28 28 28 28 28 28 28 49 ...        $ COUNTRY : Factor w/ 2 levels "","AU","US",..: 8 8 8 8 8 8 8 8 8 8Thanks for any help
> 
> 
> 	[[alternative HTML version deleted]]
> 
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-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Office: A 4.23
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com