calculate the averages of non-squared matrix blocks

Question

LH 2023-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/2014436-calculate-the-averages-of-non-squared-matrix-blocks

回答： Dyuman Joshi 2023-8-29

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Hi,

I have a non-squared matrix with a dimension of

and I would like to calculate the averages of each

block so I can get a

average vector. A schematic explanation is shown below:

The matrix and the attempt I have is the following:

close all;
clear all;
%define the 12x4 matrix
A = [1 0 2 0;
    0 1 3 0 ;
    1 1 0 0 ;
    0 2 3 1 ;
    3 2 3 0 ;
    0 1 1 2 ;
    3 1 0 2 ;
    0 0 1 0 ;
    2 1 3 1 ;
    3 2 0 0 ;
    0 0 2 0 ;
    1 3 0 2];
%calculate the average of A for each 4x4 block
Points = 4;
for irow = 1:Points:size(A,1)
    for icol = 1:size(A,2)
        block_sum = 0;
        block_sum = block_sum + A(irow, icol);
    end
end
block_avg                   = block_sum / Points;
block_row                   = ceil(irow / Points);
block_col                   = ceil(icol / Points);
ave_A(block_row, block_col) = block_avg;

Any help would be appreciated. Thanks.

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Answer 1

Image Analyst 2023-8-29

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在 MATLAB Online 中打开

Here is one way (there are others):

% Define the 12x4 matrix
A = [1 0 2 0;
    0 1 3 0 ;
    1 1 0 0 ;
    0 2 3 1 ;
    3 2 3 0 ;
    0 1 1 2 ;
    3 1 0 2 ;
    0 0 1 0 ;
    2 1 3 1 ;
    3 2 0 0 ;
    0 0 2 0 ;
    1 3 0 2];
%calculate the average of A for each 4x4 block
Points = 4;
index = 1;
for iRow = 1:Points:size(A,1)
    ave_A(index) = mean(A(iRow:iRow+Points-1, :), 'all');
    index = index + 1;
end
ave_A % Display in command window.
ave_A = 1×3
    0.9375    1.1875    1.2500

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Answer 2

Dyuman Joshi 2023-8-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2014436-calculate-the-averages-of-non-squared-matrix-blocks#answer_1296351

在 MATLAB Online 中打开

A = [1 0 2 0;
    0 1 3 0 ;
    1 1 0 0 ;
    0 2 3 1 ;
    3 2 3 0 ;
    0 1 1 2 ;
    3 1 0 2 ;
    0 0 1 0 ;
    2 1 3 1 ;
    3 2 0 0 ;
    0 0 2 0 ;
    1 3 0 2];
%nxn block
n=4;
%Use conv2 to get mean of every nxn block of input array
B = conv2(A,ones(n),'valid')/n^2;
%Select every nth element
out = B(1:n:end)
ans = 3×1
    0.9375
    1.1875
    1.2500