[R] built a lower triangular matrix from dataframe

[David Winsemius]

On Feb 15, 2012, at 11:47 AM, nymphita wrote:

> Hi Tsjerk!
>
> Thanks for your quick reply!
> It's a nice way to built a lower triangular matrix with zeros in the
> diagonal, but what I can't work out is *how to include the values of  
> the
> third column of the dataframe inside the matrix*.
>
> I just realized that I forgot to explain something about the  
> dataframe  (the
> meaning of i, j ,k) in my post:
> The data frame has three columns, the first one (i) corresponds to  
> the "row
> subscript" of the matrix [i, ], the second one (j) corresponds to the
> "column subscript" of the matrix [ ,j], and the third column in the
> dataframe (k) is the value that has to be in the matrix (in position  
> [i,
> j]).
>
> http://r.789695.n4.nabble.com/file/n4391099/df.png

You might be able to create a matrix of zeros withthis untested code:

zmat <- matrix(0, ncol=1+max(j), nrow=1+max(i) )

# Then populate it with:

zmat[ cbind(i,j) ] <- k

(Tested solutions offered when reproducible code is posted. Png images  
of data on Nabble do not count as reproducible code in my estimation.  
I cannot understand why you wouldn't post that data in the body of the  
message.)

-- 
david.

>
> The result is that the dataframe gives you a position and a value in  
> a lower
> triangular matrix:
>
> http://r.789695.n4.nabble.com/file/n4391099/matrix.png
>
> Still can't find a solution to built a lower triangular matrix with  
> the
> specific values of that dataframe...
> Any more ideas, please?
>
>
>
> --
> View this message in context: http://r.789695.n4.nabble.com/built-a-lower-triangular-matrix-from-dataframe-tp4390813p4391099.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT