Hi John,
I would guess that your Color column is a factor, with three levels
("RED","BLUE","WHITE"), which means that they will all be included in
the output of a table() call, even if they are empty. Try
dataset <- transform(dataset, Color=as.character(Color))
or something similar and then create the table.
/Fredrik
On Fri, Aug 21, 2009 at 11:08 PM, jlwoodard<john.wood...@wayne.edu> wrote:
>
> I have a data set similar to the following:
>
> Color Score
> RED 10
> RED 13
> RED 12
> WHITE 22
> WHITE 27
> WHITE 25
> BLUE 18
> BLUE 17
> BLUE 16
>
> and I am trying to to select just the values of Color that are equal to RED
> or WHITE, excluding the BLUE.
>
> I've tried the following:
> myComp1<-subset(dataset, Color =="RED" | Color == "WHITE")
> myComp1<-subset(dataset, Color != "BLUE")
> myComp1<-dataset[which(dataset$Color != "BLUE"),]
>
> Each of the above lines successfully excludes the BLUE subjects, but the
> "BLUE" category is still present in my data set; that is, if I try
> table(Color) I get
>
> RED WHITE BLUE
> 82 151 0
>
> If I try to do a t-test (since I've presumably gone from three groups to two
> groups), I get:
> Error in if (stderr < 10 * .Machine$double.eps * max(abs(mx), abs(my)))
> stop("data are essentially constant") :
> missing value where TRUE/FALSE needed
> In addition: Warning message:
> In mean.default(y) : argument is not numeric or logical: returning NA
>
> and describe.by(score,Color) gives me descriptives for RED and WHITE, and
> BLUE also shows up as NULL.
>
> How can I eliminate the BLUE category completely so I can do a t-test using
> Color (with just the RED and WHITE subjects)?
>
> Many thanks in advance!!
>
> John
>
>
>
> --
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> Sent from the R help mailing list archive at Nabble.com.
>
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