[R] poly objects as data frame columns
Ulrike Grömping
groemp at tfh-berlin.de
Fri Jul 17 18:54:30 CEST 2009
Dear UseRs,
I just learnt that the number of columns of a data frame is not always what
I thought it to be, and I wonder where I should have learnt about this.
Consider the following example:
dat <- data.frame(X1=1:10, X2=LETTERS[1:10])
ncol(dat) ## evaluates to 2 (of course)
dat$X1poly <- poly(dat$X1,3)
dat ## five columns displayed
ncol(dat) ## evaluates to 3
colnames(dat) ## three names (third is X1poly)
colnames(dat)[3] <- "newname"
dat ## all three previous X1poly columns renamed
This appears intentional, as it treats the column names reasonably. Where is
it documented ? Are there any other scenarios for which the number of
columns displayed when printing a data frame does not coincide with ncol ?
Regards, Ulrike
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