[R] built a lower triangular matrix from dataframe

[Tsjerk Wassenaar]

Hi Nymphita,

?upper.tri

x <- as.data.frame(matrix(1:6,6,6))
x[upper.tri(x,diag=TRUE)] <- 0
x

Cheers,

Tsjerk

On Wed, Feb 15, 2012 at 4:33 PM, nymphita <nymphita at gmail.com> wrote:
> Hello!
>
> I'm trying to build a lower triangular matrix (with zeros in the diagonal)
> from a particular dataframe.
>
> The matrix I have to construct has 203 rows and 203 columns and that makes
> 20503 values to be included within (that's why I can't do it manually).
>
> To illustrate the dataframe I have, I'll give you an example of a dataframe
> and matrix with dimensions 6x6 (to make it shorter!)
>
> My dataframe looks more or less like this (but longeeeer):
> (i= number of row, j=number of column, k=value to be included in the matrix)
>
> http://r.789695.n4.nabble.com/file/n4390813/df.png
>
> An the matrix I should look like this:
>
> http://r.789695.n4.nabble.com/file/n4390813/matrix.png
>
> Can anyone help me about how to do it?
>
> I'm a new R user, and I've tried several combinations of diag(),
> lower.tri(), matrix(), etc. without any luck... and I don't know if I'm
> unaware of a command that can work this out.
>
>
>
> --
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>
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-- 
Tsjerk A. Wassenaar, Ph.D.

post-doctoral researcher
Molecular Dynamics Group
* Groningen Institute for Biomolecular Research and Biotechnology
* Zernike Institute for Advanced Materials
University of Groningen
The Netherlands