> On Aug 23, 2016, at 3:03 PM, Gang Chen <gangch...@gmail.com> wrote:
>
> This is a simple question: With a dataframe like the following
>
> myData <- data.frame(X=c(1, 2, 3, 4), Y=c(4, 3, 2, 1), Z=c('A', 'A', 'B',
> 'B'))
>
> how can I get the cross product between X and Y for each level of
> factor Z? My difficulty is that I don't know how to deal with the fact
> that crossprod() acts on two variables in this case.
>
Just make a function that takes a dataframe and does a crossprod on two of its
columns.
--
David Winsemius
Alameda, CA, USA
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