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Re: Intepolation of an array with missing points

  • To: mathgroup at
  • Subject: [mg62341] Re: [mg62323] Intepolation of an array with missing points
  • From: "Yasvir A. Tesiram" <tesiramy at>
  • Date: Mon, 21 Nov 2005 03:54:24 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at


1. I suspect that when you Import the data, empty entries will be set to 
Null. Now you have to make the decision as to what to do with the Null 


lt={Null, 1, 2.0, 3.0 , Null, 4.0}


lt/.Null -> 0.0


Alternatively, you may want to make it the average of the two numbers 
flanking it.
Either way, Interpolation doesn't care and will represent your data 
Since your data will be a list of lists, you will want to Interpolate over 
each row and each column. Here is some code that Interpolates an arrayed 
data set and allows you to build a bigger data set.

sharpenCSI[data_, origSize_, finalSize_] := Module[{int},
     int = Interpolation /@ data;
     Table[#[i], {i, 1, origSize[[2]],
                 finalSize[[2]]}] & /@ (Interpolation /@ (Transpose[
                 Table[#[i], {i, 1, origSize[[1]],
                         origSize[[1]]/finalSize[[1]]}] & /@ int])) //

You can use ListContourPlot, ListDensityPlot etc to visualize such data 
Hope this helps.


On Sat, 19 Nov 2005, dkjk at wrote:

> Hi,
> I have an array representing the heights of a surface over the x-y
> plane. Unfortunately, the heights at several points are unknown so have
> been replaced by empty strings. For an example, see
> arr = Import["output.csv"] // MatrixForm
> My ultimate goal is to create an interpolating function of this data
> which will allow me to produce a contour plot. As a very inexperienced
> user of Mathematica, my initial thoughts have been someting like this:
> 1. Convert arr to an list of 3-tuples, ignoring the empty entries. (not
> sure how to do this)
> 2. Use Interpolation to create an InterpolatingFunction which can be
> plotted in ContourPlot.
> Does anyone know of a simple method to achieve 1. and whether or not 2.
> will work in this case?
> Thanks.
> James

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