Re: [R] Contour - data points not in ascending order?

From: Ted Harding <Ted.Harding_at_manchester.ac.uk>
Date: Tue, 29 Jun 2010 10:36:22 +0100 (BST)


On 29-Jun-10 08:53:48, Kirkeby wrote:
> Hi again.
>
> I have made an example of my data:
>
> x<-c(1,2,3,4,1,2,3,4,1,2,3,4,1,2,3,4)
> y<-c(1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4)
> z <- c(12,23,23,42,12,1,1,32,5,45,65,76,32,21,23,43)
> data <- unique(cbind(x,y,z))
> contour(x,y,z, col="red", xlim=c(0,1), ylim=c(0,1), labcex=0.7,
> cex="12")
>
> -which gives an error message.
>
> /CK

Have a close look at ?contour

x,y: locations of grid lines at which the values in 'z'

          are measured. These must be in ascending order. z: a matrix containing the values to be plotted

         ('NA's are allowed).

Notice that 'contour' interprets the 'z' matrix as a table

     of 'f(x[i], y[j])' values, so that the x axis corresponds
     to row number and the y axis to column number, with
     column 1 at the bottom, i.e. a 90 degree clockwise
     rotation of the conventional textual layout.

So your data above:

  x<-c(1,2,3,4,1,2,3,4,1,2,3,4,1,2,3,4)
  y<-c(1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4)
  z <- c(12,23,23,42,12,1,1,32,5,45,65,76,32,21,23,43)

correspond to:

  x <- c(1,2,3,4) ; y <- c(1,2,3,4)

(i.e. locations of grid *lines*, not points) with z being the matrix

  12 12 5 32
  23 1 45 21
  23 1 65 23
  42 32 76 43

i.e.

  z <- matrix(c(12,23,23,42,12,1,1,32,5,45,65,76,32,21,23,43),ncol=4)

Then

  contour(x,y,z)

should do the job!

Ted.



E-Mail: (Ted Harding) <Ted.Harding_at_manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861
Date: 29-Jun-10                                       Time: 10:36:20
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