Extract X number of elements in 3D matrix based on another matrix

Hello,

I have a 3D Matrix A (3x3x5) that is sorted in descending order and another Matrix B (3x3) which has the first X number of elements in Matrix A that I would like to extract and store in a blank matrix C (3x3x5). Matrix B has different first elements to extract, so I would like the rest of the elements in the 3D matrix C to be zero if there isn't anything copied from A. Let's say there are 2 values that I want to extract at element 1x1x1:5, then cell 1x1x1:2 in Matrix C will be 10; 5; 0; 0;0

Example of Matrix A and B: A=randi(10,3,3,5); B=[NaN 2 1; 2 NaN 2;NaN 4 3];

Thank you for the help.

Answer 1

[Andrei Bobrov]

A=randi(10,3,3,5); 
B=[NaN 2 1; 2 NaN 2;NaN 4 3];

[m,n,k] = size(A);
B(isnan(B)) = 0;
out = permute(reshape((1:k)'*ones(1,m*n) <= B(:)',[],m,n),[2,3,1]).*A; %2016b and later
out = permute(reshape(bsxfun(@le,(1:k)'*ones(1,m*n),B(:)'),[],m,n),[2,3,1]).*A; %2016a and earlier

[Vesp]

Thank you very much for your help Andrei! This is useful code to learn for the future :)

[Vesp]

Andrei I was wondering if you could break down exactly what this code does. It is extracting correctly, but for some reason when I apply it to my code I am not getting the correct answer.

The main idea of my code is to sort total IVT and then sort the x and y component, then use this piece of code to extract the "top N" values defined in a matrix (in this example Matrix B). When I calculate the magnitude of the separate x and y components they do not match that of the total IVT. There is a difference of up to 50 between some of the elements.

If it helps to see the entire code I have asked a question in the following link. My effort to figure this out was of no avail. I appreciate the help and time.

https://www.mathworks.com/matlabcentral/answers/345890-code-concerning-top-n-ivt-and-sorting-x-and-y-component-like-that-of-top-n-ivt-not-correct