Check if sub-block in matrix meets a condition?
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Andrew Poissant
le 14 Sep 2018
Modifié(e) : Adam Danz
le 14 Sep 2018
I have a 7x10 matrix of integer values (see attached .mat file). I want to check if a block inside the matrix (lets say 2x2) meets a condition. For example: lets say I want to see if any 2x2 block in the attached matrix all have values of 2. If there is such a 2x2 block within the matrix then return a value of 1 (true), if not return value of 0 (false). In the matrix attached, there is a 2x2 block of 2s so the output of what I am looking for in this example would be 1 (true). I would also like to generalize this for any size block.
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Adam Danz
le 14 Sep 2018
Modifié(e) : Adam Danz
le 14 Sep 2018
Here's a solution that involves a loop but it's very fast. This searches for a submatrix key within a larger matrix main. Let's say key is 2x2; it will loop through all neighboring columns of main searching for key within each pair of neighboring columns. This works no matter what size key is as long as it has less columns than main. The variable isInMain will be a logical indicating whether key is in main.
It also uses strfind() which strangely operates on doubles.
Example that results in 'true'
main = randi(10, [7,10]);
key = main([3,4],[4,5]);
Example that results in 'false'
main = randi(10, [7,10]);
key = [40, 50; 11 9];
The code
isInMain = false;
finished = false;
colIdx = 0;
searchFor = true(1, size(key,1));
while ~isInMain && ~finished
colIdx = colIdx + 1;
currColumns = colIdx : colIdx + size(key,2) - 1;
ismem = ismember(main(:,currColumns), key, 'rows');
isInMain = ~isempty(strfind(ismem', searchFor));
finished = max(currColumns)+1 > size(main, 2);
end
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Andrew Poissant
le 14 Sep 2018
Modifié(e) : Andrew Poissant
le 14 Sep 2018
2 commentaires
Adam Danz
le 14 Sep 2018
How are you using the outputs of intersect() to determine if your submatrix is within the main matrix?
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