R help - Sep 2011 - Including only a subset of the levels of a factor XXXX

Hello everyone,

I have the following factor:

levels(pp_income)
 [1] ""       "1"      "2"      "3"     
"4"      "5"      "6"      "7"
 [9] "8"      "9"      "Renter"

I want to subset so that only values 1:9 are included. I have the following:
> income<-pp_income[pp_income %in% c(1:9)]
>
> levels(income)
 [1] ""       "1"      "2"      "3"     
"4"      "5"      "6"      "7"
 [9] "8"      "9"      "Renter"

Why is this not working and can someone please suggest a solution?

Thank you!

Dan

	[[alternative HTML version deleted]]

Dropping all occurences of a factor does not drop that level. This actually
turns out to be much more useful than it first might appear, but if you
really need to get around it, it can be done.

Look at this toy example:

R> x =
factor(c("A","B","C","A","B","C","C"))
R> x
[1] A B C A B C C
Levels: A B C

R> x[x != "C"]
[1] A B A B
Levels: A B C

R> y = factor(1:10)
R> y
[1] 1  2  3  4  5  6  7  8  9  10
Levels: 1 2 3 4 5 6 7 8 9 10

R> y[y != 5]
[1] 1  2  3  4  6  7  8  9  10
Levels: 1 2 3 4 5 6 7 8 9 10

If you really need the level change, search the history of this list for
mentions of "recode" (it comes up quite frequently)

Michael

On Thu, Sep 1, 2011 at 2:59 PM, Dan Abner <dan.abner99@gmail.com> wrote:
> Hello everyone,
>
> I have the following factor:
>
> levels(pp_income)
>  [1] ""       "1"      "2"      "3"
"4"      "5"      "6"      "7"
>  [9] "8"      "9"      "Renter"
>
> I want to subset so that only values 1:9 are included. I have the
> following:
>
> > income<-pp_income[pp_income %in% c(1:9)]
> >
> > levels(income)
>  [1] ""       "1"      "2"      "3"
"4"      "5"      "6"      "7"
>  [9] "8"      "9"      "Renter"
>
> Why is this not working and can someone please suggest a solution?
>
> Thank you!
>
> Dan
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On Sep 1, 2011, at 2:59 PM, Dan Abner wrote:
> Hello everyone,
>
> I have the following factor:
>
> levels(pp_income)
> [1] ""       "1"      "2"      "3" 
"4"      "5"      "6"      "7"
> [9] "8"      "9"      "Renter"
>
> I want to subset so that only values 1:9 are included. I have the  
> following:
>
>> income<-pp_income[pp_income %in% c(1:9)]
>>
>> levels(income)
> [1] ""       "1"      "2"      "3" 
"4"      "5"      "6"      "7"
> [9] "8"      "9"      "Renter"
>
> Why is this not working
Actually it could be that it did succeed but you just have levels  
attributes that are unpopulated in your result. Try:

table{income)

If that looks correct, then do this:

income <- factor(income)  # will drop unused levels

> and can someone please suggest a solution?
If on the other hand you got the wrong values then there was an  
undesired coercion of either 'factor' class to 'numeric' or of  
'numeric' to 'character'. I am fairly sure this will remove any
ambiguity:

income<-pp_income[as.character(pp_income)
                         %in% as.character(1:9)]

(You would still get the puzzling extra levels if you looked with  
levels(income).)
>
> Thank you!
>
> Dan
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT