Ceate a x b matrix (or 2D array) from 2 1Darrays, and populate each cell from another array

So I have 3 arrays; say a,b,c. a and b represent distances, and c represents a variable with a specific value at the point (a,b).

I have been trying to create a matrix which comprises of (b x a) cells, and the populate it with the values of c, in order to then image, heatmap it etc.

However the issue I have having is that there are many repeating values of a and b; a stays fixed and it then iterates across all values of b, then moves onto the next value of a, and so forth. The range of a and b is fixed and always iterate across equally spaced values though.

Below is the code I have created for this. So for it seems to not to work and I am out of ideas.

z_true_len = length(unique(a)); %number of z distances
r_true_len = length(unique(b)); %number of r disatances
data_matrix = zeros(r_true_len,z_true_len); %create r x z matrix, full of 0s
z_past = 0; 
r_past = 0;
z_count = 1;
r_count = 1;
for count = 1: length(a)
    z_current = a(count);
    if z_past ~= z_current
        data_matrix(1:z_count) = c(count);
        z_past = z_current;
        z_count = z_count + 1;
        r_count = 1;
    else
        data_matrix(r_count:z_count) = c(count);
        r_count = r_count + 1;
    end      
end    

data_matrix

I have also tried the simplier:

a = [1 1 1 1 2 2 2 2 3 3 3 3];
b = [1 2 3 4 1 2 3 4 1 2 3 4];
c = [0 2 1 0 0 4 6 8 4 2 0 0];

z_true_len = length(unique(a));
r_true_len = length(unique(b));
data_matrix = zeros(r_true_len,z_true_len);

for count = 1:length(a),
    data_matrix(b(count),a(count)) = c(count);    
end  

figure;
imagesc(data_matrix)

However this will only work if a,b and c contatin interger values, which sadly they do not.

Answer 1

[Ahmet Cecen]

 [X,Y] = meshgrid(xgv,ygv)

is your friend.

You can also do it another way, let say your x range is 1 to 5 and y range is 1 to 6, and I am also assuming x goes 1 1 1 1 1 1 while y goes 1 2 3 4 5 6 and so on:

 X=reshape(x,[6 5]);
 Y=reshape(y,[6 5]);
 C=reshape(c,[6 5]);

 surf(X,Y,C);

[David]

so i tried

[B,A] = meshgrid(r_true_len, z_true_len);

for count = 1:length(a),
    [b(count),a(count)]=c(count);
end

and got "Indexing cannot yield multiple results." as an error

[Ahmet Cecen]

You are supposed to use the vectors not the lengths.

Try reshaping C instead as above, then you can use the x and y vectors as axis labels on the plot instead, since you said they are not integers. Afterwards:

 surf(C)

[David]

Size arguments must be real integers.

Is the error I get when reshaping, seeing how the max values arent integers

[Ahmet Cecen]

 C=reshape(c,[r_true_len z_true_len]);

I don't see why the above shouldn't work.

[David]

yes that works! however it seems a tad displeasing to the eye, could you point me in the right direction if theres online documentaion on editing how the surf looks on output? :)

you are a lifesaver

[Ahmet Cecen]

I would avoid trying to edit it programmatically. Use the GUI after surf to modify the colors, axes etc, then use file->generate code to spit out a function that will have your visual modifications coded in automatically. You would then use the new function to plot subsequent results.

Check:

http://www.mathworks.com/help/matlab/creating_plots/plotting-tools--interactive-plotting.html#f9-43442

http://www.mathworks.com/help/matlab/creating_plots/saving-your-work.html#f9-46417

[David]

I owe you a pint good sir! have a good day :)