[R] Fw: removing factor values in the main data frame

[Jeff Newmiller]

I advocate not converting to factor in the first place.  Delay that until you won't be wanting specific levels to be accounted for. 
-- 
Sent from my phone. Please excuse my brevity.

On March 1, 2016 9:33:31 AM PST, 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."
>
>------------------------------------
>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
>
>  
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>
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>and provide commented, minimal, self-contained, reproducible code.

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