For contour plots, some of the contour functions in graphics packages
(lattice for one IIRC) are pretty good at understanding that columns in
a matrix correspond to x,y, and z values already.
********
There are many ways to do this in R. For very simple problems, this one
is convenient:
library(ecodist)
newdata <- crosstab(mydata$x, mydata$y, mydata$z)
For more complicated problems, reshape is very powerful.
Sarah
On Tue, Dec 14, 2010 at 5:13 PM, jonathan <jon_at_than.biz> wrote:
>
> That's so weird, I just signed up on here to ask exactly the same
question!
>
> However, I think my issue is like Jessica's who says that her data is
like
> that, not actually that...
>
> So the issue is not in generating that data on-the-fly but in
transforming
> it from a data frame to a matrix.
>
> As a more concrete example, I have read the following data in from a file
> (around 300,000 rows):
>
> x y z
> 0 0 687
> 0 1 64
> 0 2 71
> 0 3 55
> 0 4 52
> 0 5 51
> 0 6 38
> 0 7 38
> 0 8 54
> 0 9 49
> .........
> .........
> .........
> 304979 282977 1
> 351377 1547980 1
> 383835 1740541 1
> 418133 6024710 1
> 421549 1028572 1
> 471314 1751836 1
> 579602 1817393 1
> 713515 5524385 1
>
>
> So what I want to do is transform this into a matrix where at
position (x,y)
> in the matrix I have value z. I am doing this so that I can then do a
> filled.contour plot on the data.
>
> I think this is the same as what Jessica is asking...
>
> Regards and many thanks,
>
> Jonathan
> UCL Computer Science
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