[R] Creating subsets with factors

[Liaw, Andy]

[snipped...]

> I have not needed to use c(f1, f2) but it seems to me that 
> Peter's example points out more a deficiency in c or the need 
> for another binding function for this case (which can be done 
> with factor(c(as.character(f1),as.character(f2))) depending 
> on how NAs are handled.

More often than I'd like, I have to combine several related data frames
together.  The following showed that the rbind method for data frames does
do a reasonable job:

# Suppose dat1 and dat2 are two data frames with same variables.
> dat1$ind <- factor(rep("dat1", nrow(dat1)))
> dat2$ind <- factor(rep("dat2", nrow(dat2)))
> dat <- rbind(dat1, dat2)
> levels(dat$ind)
[1] "dat1" "dat2"

> Frank Harrell

[more snipped...]

Andy

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