[R] Odp: Data frame with 3 columns to matrix

[Michael Bach]

Petr PIKAL <petr.pikal at precheza.cz> writes:

> Hi
>
> r-help-bounces at r-project.org napsal dne 19.04.2011 09:46:47:
>
>> 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
>>       (x)
>> 
>> This example is just for illustration.  The resulting matrix should have
>> more numeric values than NA's.
>
> I am not sure if this is the solution you want
>
> tab<-xtabs(z~x+y, data=df)
> tab[tab==0]<-NA
>

This looks right, but the resulting table does not have rows == columns
and there are also no missing values (0 or NA) which should be there.  I
think I did not make myself clear, please see also my reply to the
previous answer to my question by David Winsemius.

Thanks for your reply though!