[R] built a lower triangular matrix from dataframe

[nymphita]

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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