MATLAB: Problem with nested loop

if statement and for loop

Hi, I am trying to write a code with nested for loop and if statement. I want to create a matrix in such way that, for one value of y, I have different values of x and z, and again for another value of y, I have same values for x but different values of z.
load a.dat;
x=a(:,1);
y=a(:,2); z=a(:,3); for j=min(y):1:max(y)
    for i=1:10
        if  j=10
            A(:,i)=z(i)
        else if 
             j=j+1  
         end
end
end
I am not able to apply if statement for y.
Could anyone please help me?

Best Answer

You have x and y values, and it seems that you want to use these as indices for allocating data values into another matrix. This can be achieved very easily using sub2ind. Here is a simple demo-matrix where the first column contains row indices, the second is column contains column indices, and the third contains the data:
>> A = [2,1,5;1,3,7;2,3,0;1,1,9;2,2,4]
A =
     2     1     5
     1     3     7
     2     3     0
     1     1     9
     2     2     4
%   row   col   data
then we extract the row and column indices:
>> R = A(:,1);
>> C = A(:,2);
create the output matrix and use sub2ind to get the linear indices for those row/column indices:
>> Z = nan(max(R),max(C));
>> X = sub2ind(size(Z), R, C);
and finally use the linear indices to put the data values into their right locations:
>> Z(X) = A(:,3)
Z =
     9   NaN     7
     5     4     0
Note that MATLAB has one-based indexing, so you will need to add one to the values that you have in your example data.
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