problem with nested 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?

[Guillaume]

I don't understand your question fully, and your piece of code is incomplete, so please give at least some example of input and desired output.

[Stephen23]

This could probably be written much neater using some vectorized code, which would likely also be faster.

Instead of providing us with (broken) code to interpret, it would help us if you actually described exactly what you are trying to achieve, giving precise descriptions of the inputs and outputs.

Even better would be if you also include some test values/variables for both the input and output arrays, to give us something to test our own code with.

We know MATLAB quite well so writing the code is not a problem, but what we don't know is what you are trying to do...

For a start: how should the values of A defined? What specifies their values?

[Matlabuser]

Actually, I have to rearrange my data in a proper format. I have 24 X 3 matrix, with x,y,z values.z values are calculated on x and y values. For one value of y, I have different values of x and z, for instance, x=[0,1,2,3,4,5];y=[1,1,1,1,1,1];z=[0.1,0.4,0.3,0.5,0.9,1.1] then for other value of y, like y=2, I have same values of x but different values of z.

Now I want to rearrange the data in 6 X 4 dimension such that for y=1 and all values of x, I can put values of z in 1st column of an empty matrix. Then for second value of y, z in second column.

Hope this time I am clear.

[Stephen23]

If you upload your actual data matrix then we can try this too! Please upload the data (in a textfile or .mat file) using the paperclip button that you will find above the textbox, and note that you will need to push both buttons: Choose file and Attach file.

Answer 1

[Stephen23]

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.

[Matlabuser]

Thank you very much !!!!

Answer 2

[Søren Jensen]

A(:,i)= z(i)

do you mean A(:,i)= z(:,i) or A(:,i)= z(i,:)?

When is A defined?

i see 2 for statements and 1 if statement, and only 2 "end", so some of your code seems to be missing.. what is the purpose of the code?

[Matlabuser]

Sory, I am a bit bad in Matlab. Now probably,my question is clear