[R] Data.Frame Multiplication
ggrothendieck@yifan.net
ggrothendieck at yifan.net
Thu Apr 18 16:30:19 CEST 2002
The code below takes a matrix x and converts it to a matrix
whose columns are the pairwise columns of x. If your data comes
in a data frame,df, you can always convert it to a matrix like this:
x <- as.matrix(df)
In the code below,
zz is a matrix whose i,j-th element contains the product
of column i and column j. Extract the upper triangular
portion of this matrix and reshape that into a matrix. (You can
convert that to a data frame if you prefer.)
zz <- apply(outer(t(x),x),c(1,4),function(x)list(diag(x)))
matrix(unlist(zz[upper.tri(zz)]),nrow=nrow(x))
You might want to test this out a bit since the
construction is a bit tricky and I have not extensively
tested it.
On 18 Apr 2002 at 13:03, Christian Schulz wrote:
> Have got any R-proffessional a starting point for me
> how i can write me a function which multiply every column with
> every other column in the data.frame - indenpendent from the dim's .
>
> Thanks in advance
> regards,Christian
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