How to take the co-ordinate values in MatLab
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vigneshwaran Loganathan
on 13 Jul 2018
Commented: vigneshwaran Loganathan
on 16 Jul 2018
A = [1 0 3 3;
0 0 4 5;
5 0 98 56;
0 2 4 6]
In the above 4*4 matrix, each cell has got x and y coordinates. I need to extract the x and y co-ordinate values for the cells excepting 0.
For example, the coordinates are placed in the below manner having the zero cell omitted
x 1 1 1,....
y 1 3 4,....
Any leads?
4 Comments
Image Analyst
on 15 Jul 2018
Vigneshwaran, what a bad way to name variables! Why deliberately choose variable names that fly in the face of hundreds of years of convention? You're choosing x to be the vertical/row coordinate instead of the conventional y. And you're choosing the horizontal/column coordinate of the matrix to be y, instead of the conventional x. Why? Why do it the opposite of everyone else in the world for no reason???
By the way, if you had given the full x and y instead of just the first three numbers and ..., you could have prevented a lot of confusion.
Accepted Answer
Nanditha Nirmal
on 13 Jul 2018
Hi,
The code below will give you the coordinates you want. This is what you would want to do:
A = [1 0 3 3;0 0 4 5;5 0 98 56; 0 2 4 6];
x=[];
y=[];
for i=1:4
for j=1:4
if A(i,j) ~= 0
x=[x ;i];
y=[y ;j];
end
end
end
2 Comments
Adam Danz
on 15 Jul 2018
Edited: Adam Danz
on 15 Jul 2018
You can avoid both for-loops and speed up the code with
%Your data (y values)
A = [1 0 3 3;0 0 4 5;5 0 98 56; 0 2 4 6];
% Transpose A (to match your example)
aT = A';
% Your x values
x = repmat((1:size(aT,1))', 1, size(aT,2));
y = repmat(1:size(aT,1), size(aT,2), 1);
% Identify where A==0
zeroIdx = aT==0;
% Extract coordinates where A~=0
xCoord = x(~zeroIdx);
yCoord = y(~zeroIdx);
More Answers (2)
Adam Danz
on 13 Jul 2018
If I'm understanding correctly, your matrix A are all y values and the row indices are the X values (based on your comments above).
%Your data (y values)
A = [1 0 3 3;0 0 4 5;5 0 98 56; 0 2 4 6];
% Your x values
x = repmat((1:size(A,1))', 1, size(A,2));
% Identify where A==0
zeroIdx = A==0;
% Extract coordinates where A~=0
xCoord = x(~zeroIdx);
yCoord = A(~zeroIdx);
% Test: draw your data, circle the chosen coordinates
figure;
plot(A);
hold on
plot(xCoord, yCoord, 'ko')
2 Comments
Adam Danz
on 15 Jul 2018
Nanditha's code gives you the index values. The for-loops in her code record the values of i and j which are index values of A. My code provides the index values for x and the 'A' values for y which is what I thought you were describing by, " if you plot the matrix, the output will have x,y and the index values".
See the comment I left under Nanditha's solution for a simplification.
Image Analyst
on 15 Jul 2018
Personally I'd use meshgrid() - a useful function that you might want to learn about:
[rows, columns] = size(A)
[x, y] = meshgrid(1:columns, 1:rows)
mask = A~=0
x = x(mask)
y = y(mask)
2 Comments
Adam Danz
on 15 Jul 2018
Vigneshwaran, this is the fastest, simplest solution. However, if you want it to conform to your example, you'll need to transpose A and switch the values of x and y.
aT = A';
[rows, columns] = size(aT)
[y, x] = meshgrid(1:columns, 1:rows)
mask = aT~=0
x = x(mask)
y = y(mask)
But reconsider the names of your x and y variables as suggested by Image Analyst above.
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