Generate 1 matrix from 3 data columns

I need advice and hopefully someone out there can help me. I have 3 columns of numerical data with n rows. All three columns will always have the same number of rows, but this can range between 2 and 10000 for a given data set. The example shows the kind of data I'm working with, where the first column lists X-coordinates, the second column lists Y-coordinates, and the third column lists the measured value at that x,y pair.

Example data:

   X-Coord       Y-Coord        Data
   1.00000       1.00000       0.12240
   2.00000       1.00000       0.36649
   3.00000       1.00000       0.11111
   1.00000       2.00000       0.19834
   2.00000       2.00000       0.56791
   3.00000       2.00000       0.94876
   1.00000       3.00000       0.22284
   2.00000       3.00000       0.13486
   3.00000       3.00000       0.00273

What I want is to turn Column 3 into a matrix like the one below

Data Output:

   0.22284   0.13486   0.00273
   0.19834   0.56791   0.94876
   0.12240   0.36649   0.11111

I feel like it should be possible and relatively simple, but I'm running into trouble. I tried starting by building a square matrix, and filling it point by point but with more rows:

 Data = zeros(3)
 Data(1,1) = Data(7)
 Data(2,1) = Data(4)
 Data(3,1) = Data(1)

but this becomes cumbersome and time consuming as the number of rows increase. I was considering building a loop to read X, Y, and Data and fill the matrix point by point, but I'm not sure where to begin with that.

Answer 1

[Jan]

X = [1,2,3,1,2,3,1,2,3]
Y = [1,1,1,2,2,2,3,3,3]
V = [0.12240, 0.36649, 0.11111, 0.19834, 0.56791, 0.94876, 0.22284, 0.13486, 0.00273]

nX = max(X);
nY = max(Y);
R  = zeros(nX, nY);
R(sub2ind(size(R), nY+1-Y, X)) = V;

Answer 2

[Geoff Hayes]

Jess - if z is your third column, then you could do something like

 flip(reshape(z, [3 3])',1)

We re-shape z from a 9x1 to a 3x3 array. We then transpose it (with the apostrophe) and then flip it in the first dimension to flip the order of elements.

i.e.

>> z            [
                  0.1224
                 0.36649
                 0.11111
                 0.19834
                 0.56791
                 0.94876
                 0.22284
                 0.13486
                 0.00273];

>> flip(reshape(z, [3 3])',1)

ans =
                 0.22284                   0.13486                   0.00273
                 0.19834                   0.56791                   0.94876
                  0.1224                   0.36649                   0.11111

[Jess]

Thanks for the quick response. I'm not sure why but I'm getting an error message saying "Undefined function 'flip' for input arguments of type 'double'." even though the help page for flip specifically lists double under the data types.

[Chad Greene]

The flip function was introduced in 2013b. If you have an older version you can do

 flipud(reshape(z,[3 3])')

But with that solution you have to be careful that the x and y coordinates are perfectly regular.

Answer 3

[Chad Greene]

I think you can do this with xyz2grid. Syntax is simply

Data = xyz2grid(Column1,Column2,Column3);

[Jess]

Thanks for the quick response, I've never actually used the File Exchange before. Do I need to save the matlab files in the zip folder to a specific directory?

[Chad Greene]

Hi Jess,

Yeah, unzip the folder and put it somewhere Matlab can find it. There are a number of ways to do that, but the easiest is just to put the xyz2grid.m file in your current working directory.