[R] merge

[juli g. pausas]

Dear R-users,
I'm trying to merge 2 data.frames that have different number of rows,
with a common column. Is this possible? Here a simple exemple, with the
error that I get:

a <- 1:20
b <- 21:40
ab <- data.frame(a, b)
a <- 1:40
c <- 41:80
ac <- data.frame(a, c)
rm(a, b, c)
zz <- merge(ab, ac, by.x=ab$a, by.y=ac$a)

Error in fix.by(by.x, x) : `by' must match numbers of columns

What's wrong? Any suggestion?
I'm using R 1.4.1 under MS windows
Thanks

Juli

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