Split big matrix in many submatrices having same size
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Hello,
I have a big matrix 396*2600 and I want to split it to many matrices 30*120 as follow : (let's consider this exemple on a small matrix A ans split it to 3*2 matrices):
A = [1 9 17
2 10 18
3 11 19
4 12 20
5 13 21
6 14 22
7 15 23
8 16 24];
results wanted: A1 = [1 9
2 10
3 11]
A2 = [9 17
10 18
11 19]
A3 = [2 10
3 11
4 12]
A3 = [10 18
11 19
12 20] and so on ...
Remarks: I need a solution without for loop, I'm looking for a Matlab command giving this results.
Thanks
6 Comments
Answers (2)
John D'Errico
on 4 Nov 2022
Edited: John D'Errico
on 4 Nov 2022
So many times this gets asked for. DON'T DO IT. Instead, learn to use arrays, of many types. For example, just make it into a 3 dimensional array, where each plane of that array is one of the desired sub-arrays. That requires relatively little more than understanding how to index arrays.
A = [1 9 17
2 10 18
3 11 19
4 12 20
5 13 21
6 14 22
7 15 23
8 16 24];
Here you want to generate all 3x2 contiguous subarrays. The size of A is
[r,c] = size(A)
So there will be 6*2 such 3x2 sub-arrays to generate.
Where are the elements of A stored in memory? In what order? Understanding this, and how tools like sub2ind work in MATLAB allows you to build these arrays easily.
ind1 = (1:3)' + [0,r];
ind2 = (1:r-2) + r*[0:c-2]';
B = reshape(A(ind1(:)-1 + ind2(:)'),3,2,[]);
Now it is simple to acces any of those subarrays as we have created, and do so programmatically. The array B is of size:
size(B)
There are 12 such sub-arrays.
B(:,:,1)
B(:,:,2)
B(:,:,12)
5 Comments
Jilin Zhang
on 21 Dec 2022
A=randi([0 10],426,2904)
[r1, c1]=size(A);
r2=60 %target row #
c2=240 %target column #
i=1
j=1
k=1
while i*r2<r1
while j*c2<c1
B(k,:,:)=A((i-1)*r2+1:i*r2,(j-1)*c2+1:j*c2);
j=1+j
k=1+k
end
i=1+i
end
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