Convert xy Coordinates to Matrix

I have an xy coordinates positions (100x2) and another z vector (100x1) with values corresponding to each xy coordinate. How can I make a matrix of the coordinates with the position of each coordinate having the corresponding z value? Thanks!

Answer 1

[Andrei Bobrov]

after John's comment in Image Analyst's answer:

out = accumarray([x(:),y(:)],z(:),[10 10]);

or

out = zeros(10);
out(sub2ind(size(out),x,y)) = z;

[John]

Thanks! it works now :)

[Andrei Bobrov]

Hi John! NOTE: Second part my answer (code after 'or') is the same as the Image Analyst' answer...

[John]

Now I get it, thanks for the clarification.

[cecilia dip]

Hi, I have to do the same thing, and i've tried this, but my coordinates (x,y) are negative and non-integer numbers, as they are latitude,longitude.. how can i do this? I want a plot where for each(lat,long) i can have my Z value (in a color scale, as i will compare it with interpolation methos later). Thank you!

Answer 2

[Image Analyst]

Try this:

% Setup / initialization.
% Start out matrix as zeros.
m = zeros(20,10);
% Generate 100 random coordinates.
xy = int32(randi(10, 100, 2));
% Get matrix values for those x,y locations
z = randi(255, 100, 1); % 100 values.

% Now, do what the poster, John, wants to do.
% Assign the z values to the (x,y) coordinates at the corresponding row.
% E.g. m at (x(1), y(1)) will have a value of z(1).
% m at (x(2), y(2)) will have a value of z(2).  And so on.
indexes = sub2ind([20, 10], xy(:,1), xy(:,2))
m(indexes) = z

[John]

Thanks for your help, unfortunately it didn't work. Here's my data. x and y are the coordinates and z is the corresponding value for each coordinate.

x [4 7 5 9 3 5 5 2 1 1 ]

y [9 2 9 7 9 9 1 4 7 6 ]

z [1 0 1 1 1 0 1 0 1 0 ]

I wish to create a 10x10 matrix (since my xy coordinates are between 1 and 10). In this matrix, I want each coordinate, say for instance, the first xy coordinate (4,9) whose z value is 1 is shown as 1 in column 4 row 9 of the matrix.

[Image Analyst]

Of course it DOES work if you adapt it to a 10 by 10.

m=zeros(10);
indexes = sub2ind([10, 10], x, y)
m(indexes) = z

When I did my example, I picked random numbers for x, y, and z, and random sizes. You were supposed to know that and be able to make the simple adaptations yourself. But anyway, andrei did it for you so you're all set now.

[MP]

Hello, what if I have a huge matrix 2000 x 2000 full of zeros and an XY matrix with 2300 x,y values. How can I insert the value 1 in my zero matrix (2000 X 2000) where I have an x,y value (from my XY matrix)?

[Image Analyst]

That's not huge, far from it. You can do intuitive, quick and simple for loop

for k = 1 : length(xy)
    row = xy(k, 2); % y is row
    col = xy(k, 1); % x is column
    m(row, col) = 1;
end

[Luigi Izzo]

what about if xy(k,1) or xy(k,1) are negative numbers?

Thanks

[Image Analyst]

Try using a scatteredInterpolant. Demo attached.

If you still need help, attach your x, y, and z data in a new question (not here) so people can help you.

Answer 3

[Annisa Dewanti Putri]

thanks for the help