Le Fri, May 09, 2008 at 11:23:37PM -0400, Dipankar Basu a écrit :
> > ex <- data.frame(id=id,year=year,x=x)
> > ex1 <- subset(ex[which(ex$id=="A"|ex$id=="B"),])
> > tapply(ex1$x, ex1$id, mean)
> ABC
> 22.5 32.5 NA
Dear Dipankar,
The reason for this behaviour is that the class of ex$id
you need to redefine the factor on ex1$id.. cast it again as.factor to
redefine the levels.
Dipankar Basu wrote:
>
> Hi!
>
> I am using R version 2.7.0 and am working on a panel dataset read into R
> as
> a dataframe; I call it "ex". The variables in "ex" are: id year x
>
> id: a character
Because id is a factor in your data frame, and the levels (including
"C") is kept when subsetted. Here is one way to get ride of "C".
> ex1$id <- factor(ex1$id)
> tapply(ex1$x, ex1$id, mean)
AB
22.5 32.5
On Sat, May 10, 2008 at 11:23 AM, Dipankar Basu <[EMAIL PROTECTED]> wrote:
> Hi!
>
>
Hi!
I am using R version 2.7.0 and am working on a panel dataset read into R as
a dataframe; I call it "ex". The variables in "ex" are: id year x
id: a character string which identifies the unit
year: identifies the time period
x: the variable of interest (which might contain NAs).
Here is an
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