[R] [Mailman] question: contour plot for discrete data

[Spencer Graves]

Have you considered "interp", as in the following example: 

XY <- expand.grid(x=1:11, y=1:11)
XY$z <- XY$x+XY$y
contour(interp(XY$x, XY$y, XY$z))

hope this helps.  spencer graves

Thomas W Blackwell wrote:

>Dear L Z  -
>
>Before using  contour()  one needs to interpolate the z values
>to all points in a rectangular grid.  2D interpolation is not
>trivial.  The package KernSmooth (case-sensitive) will do this
>for a density estimate but not, apparently, when z values are
>given.  Perhaps packages splines or mclust will do this, although
>I haven't checked.  More likely, the functions  surf.ls(), surf.gls()
>from package spatial.
>
>Other users who are familiar with maps and geographic information
>systems (GIS) packages for R may have much better ideas for you
>than I know about.  I've never had occasion to use any of this.
>
>-  tom blackwell  -  u michigan medical school  -  ann arbor  -
>
>On Fri, 19 Dec 2003, L Z wrote:
>
>  
>
>>Question:
>> I have matrix (n x3) that represents discrete data.
>>Each row of matrix is 3-D point (x,y,z). I would like
>>to get contour map (z value) at two dimension
>>(x,y). How can I use related contour function to do
>>this job?
>>I am not sure if I clarify this question. For example,
>>we can get point (x,y)
>>at 2 dimension according to first two columns of
>>matrix. Then I want to connect
>>same value z=(x,y). Thanks!
>>  zhang
>>
>>The data file looks like this:
>>X          y               z
>>4           0.33          0.99
>>4           0.5            1.2
>>5           0.66          1.2
>>5           0.7            1.5
>>6           2               1.2
>>?
>>
>>    
>>
>
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