can this code be sped up?

I have a short program to take x-y-z (position position value) data and turn it into a matrix and then make a filled contour plot with it, i have large data sets (finished matrix is 1560 x 78). The data is listed with a fixed y for 1560 points with a changing x and z measurement, then that is repeated 77 more times with a different y. The code takes atleast 68 seconds to run depending on which computer i run it on. I was wondering if there is a way to change the code to speed it up. here is the code.

    ifilename = uigetfile;
    data=importdata(filename);
    Matrixform=data.data;
    x=Matrixform(:,1);
    y=Matrixform(:,2);
    z=Matrixform(:,3);
    i=1;
    m=length(unique(y));
    n=length(unique(x));
    yl=length(y);
    for i=1:m;
        j=1;
        for j=1:n;
            Mat(j,i)=z(j+n*(i-1));
        end
    end

[c,h] = contourf(Mat,200);

I have tried using meshgrid and griddata but the plot was smoothed too much ( i tried linear and cubic variations). i dont want to lose any detail from my data. thanks in advance

Answer 1

[Sean de Wolski]

Mat = zeros(n,m);

before the two for-loops will speed this up immensely for large [m n].

Also, you don't need to set j=1 in the first for-loop, this is done automatically on the initialization of the inner loop.

Answer 2

[Robert Cumming]

you dont appear to initialize your Mat variable, i.e.

Mat = zeros(n,m)

This should make a big difference to start with

Answer 3

[Andrew Newell]

You could replace the double loop by

Mat =  reshape(z,n,m);

EDIT: I'll bet most of the time is spent calculating 200 contours. You could try

imagesc(Mat)