[R] question on image() function?

[Luke Spadavecchia]

You could try using levelplot from the lattice package:

library(lattice)
levelplot(mcpvalue~x+y)

failing that, interpolate them to a grid using akima or fields then  
display with image

L

On 8 Nov 2007, at 18:13, Duncan Murdoch wrote:

> On 11/8/2007 11:51 AM, zhijie zhang wrote:
>> Dear friends,
>>   My dataset is like the following:
>>          x                y              mcpvalue
>> 0.4603578     0.6247629       1.001
>> 0.4603715     0.6247788        1.001
>> 0.4603852     0.6247948       1.001
>> 0.4110561     0.5664841       0.995
>>  The x and y variables are unsorted.
>>  I use the function image(x,y,mcpvalue) to generate a plot, but  
>> the error
>> is that "increasing 'x' and 'y' values are expected". So i use
>>    image(x=seq(min(x),max(x)), y=seq(min(y),max(y)),z=as.matrix
>> (result$mcpvalue))
>> to do it again, but there is still an error "dimensions of z are not
>> length(x)(-1) times length(y)(-1)".
>>   Anybody can show me how to use the image() correctly with the  
>> original x/y
>> unsorted?
>
> You can't, it doesn't know how to handle that kind of data.
>
> image() is designed to display a matrix of values.  The x and y values
> tell it where to put the rows and columns of the matrix.
>
> You have a set of points.  You need to fit a surface to them, evaluate
> the surface on a grid, and pass that to image().
>
> There are many ways to do that; the akima package has the interp()
> function for instance.
>
> Duncan Murdoch
>
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