Hi Dennis,

Thanks for your quick response and sorry for not being clear. That helped, but I need an actual matrix of e.g., 12 x 12 and those functions give me a matrix with only the "filled" locations. I need a 12 by 12 matrix with sums (0 if there's not data and the actual sum where there is) as follows:

  1 2 3 4 5 6 7 8 9 10 11 12
1 0 0 0 . . . . . .  0  0  0
2 0 0 0 .
3 0 0 0 .
.
.
10                  0 81  0
11                  0  0 30
12                 95  0  0

Any hints?

THANKS!!
Nico


-------- Original Message --------
Subject:        Re: [R] sum data from data.frame in a matrix
Date:   Wed, 23 Feb 2011 00:10:52 -0800
From:   Dennis Murphy <djmu...@gmail.com>
To:     Nicolas Gutierrez <nicol...@uw.edu>



Hi:

...and a second way, using the reshape2 package:

library(reshape2)
dcast(df, yloc ~ xloc, value_var = 'yield', fun = sum)
   yloc 10 11 12
1   10  0 81  0
2   11  0  0 30
3   12 95  0  0


Dennis

On Tue, Feb 22, 2011 at 11:30 PM, Nicolas Gutierrez <nicol...@uw.edu
<mailto:nicol...@uw.edu>> wrote:

    Hi all (again),

    I have a data frame "pop":

       xloc  yloc  yield
    1  10    12    95
    2  11    10    81
    3  12    11    20
    4  12    11    10

    And I want to get the sum of yield for the cell (pop$xloc, pop$yloc)
    in a matrix as follows:

                xloc
              10  11  12
           10 0   81  0
      yloc  11 0   0   30
           12 95  0   0


    Any ideas? thanks!

    Nico

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