[R] Data frame with 3 columns to matrix

From: Michael Bach <phaebz_at_gmail.com>
Date: Tue, 19 Apr 2011 10:46:47 +0300

Dear R Users,

Lets assume I have this data frame:

     x y z

1 1.00 5 0.5
2 1.02 5 0.7
3 1.04 7 0.1
4 1.06 9 0.4

x and y columns are sorted and the values not necessarily integers. z values are not sorted. Now I would like to create a matrix out of this with x as first column values and y as first row values. Matrix element a_11 shall be left NA. The a_ij should have the z value for the corresponding x and y pair. The result shall be some sort of a grid and then e.g. look like:

     [,1] [,2] [,3] [,4] [,5]
[1,] NA 5 6 7 9 (y)
[2,] 1.00 0.5 NA NA NA
[3,] 1.02 0.7 NA NA NA
[4,] 1.04 NA NA 0.1 NA
[5,] 1.06 NA NA NA 0.4


This example is just for illustration. The resulting matrix should have more numeric values than NA's.

I hope I made myself clear. Any hints on how to achieve this? Is there already a function that does it? All searches I did pointed me to data type frame to matrix conversion...

Kind Regards,
Michael Bach

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