R help - Nov 2007 - question on image() function?

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?
  Thanks very much.


-- 
With Kind Regards,

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[***********************************************************************]
Zhi Jie,Zhang ,PHD
Tel:+86-21-54237149
Dept. of Epidemiology,School of Public Health,Fudan University
Address:No. 138 Yi Xue Yuan Road,Shanghai,China
Postcode:200032
Email:epistat@gmail.com
Website: www.statABC.com
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:\.(:::Oooo::
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	[[alternative HTML version deleted]]

Hi

look at akima package, especially its function interp.

Petr

petr.pikal at precheza.cz

r-help-bounces at r-project.org napsal dne 08.11.2007 17:51:21:
> 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?
>   Thanks very much.
> 
> 
> -- 
> With Kind Regards,
> 
> oooO:::::::::
> (..):::::::::
> :\.(:::Oooo::
> ::\_)::(..)::
> :::::::)./:::
> ::::::(_/::::
> :::::::::::::
> 
[***********************************************************************]
> Zhi Jie,Zhang ,PHD
> Tel:+86-21-54237149
> Dept. of Epidemiology,School of Public Health,Fudan University
> Address:No. 138 Yi Xue Yuan Road,Shanghai,China
> Postcode:200032
> Email:epistat at gmail.com
> Website: www.statABC.com
> 
[***********************************************************************]
> oooO:::::::::
> (..):::::::::
> :\.(:::Oooo::
> ::\_)::(..)::
> :::::::)./:::
> ::::::(_/::::
> :::::::::::::
> 
>    [[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

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