MATLAB: Merging two arrays based on index arrays

arrayMATLABmatrixmatrix array

I have the arrays z_index = [2 3] and y_index = [4 1 5]. They store the indices of a main array x. z(z_index) = [1 3] and y(y_index) = [-2 4 2]. How do I code to find the array x = [4 1 3 -2 2] which merges the z and y arrays based on the index arrays z_index and y_index?

Best Answer

z_index = [2,3];
y_index = [4,1,5];
z(z_index) = [1,3];
y(y_index) = [-2,4,2];
x(z_index) = z(z_index); % RHS = [1,3]
x(y_index) = y(y_index)  % RHS = [-2,4,2]
x = 1×5
     4     1     3    -2     2
●

Or slightly more robustly:

x = [z(z_index),y(y_index)]; % RHS = [1,3,-2,4,2]
x([z_index,y_index]) = x
x = 1×5
     4     1     3    -2     2
●

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ZData = XYZData{:,3};

MATLAB: Meshgrid

I assume that x and y have the same values as x1 and y1, but in a different order. You could do a search for each pair (x1,y1), but it's faster to sort the coordinates and then reshape Z. Here is an example with an actual image to give you the idea:

%%Set up the problem
load mandrill
Z = X; %rename image
nrows = size(Z,1); ncols = size(Z,2);
[x1,y1] = meshgrid(1:nrows,1:ncols);
x = x1(:); y = y1(:); Z = Z(:);
% Scramble the elements.
index = randperm(numel(Z));
x = x(index); y = y(index); Z = Z(index);
%%Now the problem is set up, unscramble x and y and then reshape Z.
xy = [x y];
[~,index] = sortrows(xy,[1 2]);
x = x(index); y = y(index); Z = Z(index);
Z = reshape(Z,nrows,ncols);
image(Z)

Of course, if x and y were originally obtained from a process like that in the previous cell, you won't need to sort.

Best Answer

Related Solutions

MATLAB: I’m having trouble plotting imported xy or xyz data

MATLAB: Meshgrid

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