fill a matrix within a loop

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Enzo
Enzo 2023-4-29
评论： Enzo 2023-4-29
Hello everyone,
I am growing more confident in Matlab, thanks to community support, but sometimes I feel stucked due to very silly issues, as per the following case:
matr_counts_per_chunk = zeros(120,2752);
for col= 1:length(tr_x_ch)
matr_mat_fil_non_bool_sigle_tr = resh_matr_mat_fil_non_bool(:,col);
matr_counts_per_chunk(:,col) = sum(reshape(matr_mat_fil_non_bool_sigle_tr,[],250),2);
end
the problem is: matr_counts_per_chunk is only correctly filled in the first iteration, then I get only zeros in every 2751 left columns. This mean the for loop is actiually doing nothing/not working except for the first call.
Any help will be appreciated
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Stephen23
Stephen23 2023-4-29
"In the attachemnts you will find the actual matrix in order to run the code yourself. "
Nope: you did not include tr_x_ch as Image Analyst requested, nor have you described its size as I requested.
Enzo
Enzo 2023-4-29
编辑：Enzo 2023-4-29
hi @Stephen23 , carefully cheking my first reply, you will find 2752 in the first line. Maybe it was not so clear
tr_x_ch = 2752 is the actual reply
I have attached the file to the question

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采纳的回答

Stephen23
Stephen23 2023-4-29
编辑：Stephen23 2023-4-29
"tr_x_ch = 2752 is the actual reply"
Then tr_x_ch is a scalar. The length of a scalar is exactly 1 (by definition), so your loop will iterate exactly one time.
If that is the case, you probably want this:
for col= 1:tr_x_ch
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Enzo
Enzo 2023-4-29
@Stephen23 that's exactly why I feel like it was really easy to solve, and I am still a noob in the way to become proficient in matlab. still a long way! Thanks so much

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Image Analyst
Image Analyst 2023-4-29
Here's what I get, after adding comments and clarifying the variable names.:
fileName = 'resh_matr_mat_fil_non_bool.mat';
load(fileName) % Load "resh_matr_mat_fil_non_bool" from a .mat file.
% resh_matr_mat_fil_non_bool is a 30,000 row by 2752 column 2-D matrix.
[rows, columns] = size(resh_matr_mat_fil_non_bool)
tr_x_ch = zeros(rows, 1); % A 2752 column vector.
% Preallocate a matrix.
matr_counts_per_chunk = zeros(120, 2752);
for col = 1 : columns
% Get data into a 30,000 by 1 column vector.
thisColumn = resh_matr_mat_fil_non_bool(:, col);
% Reshape into 120 rows by 250 columns.
matrix2d = reshape(thisColumn, [], 250);
% Sum the matrix across, getting a 250 row by 1 column vector
% and put the sums into the column of matr_counts_per_chunk;
matr_counts_per_chunk(:, col) = sum(matrix2d, 2);
end
fprintf('Done!\n')
matr_counts_per_chunk has values all over the matrix, not just in the first column, so I can't reproduce what you said. It basically does what you tell it to.
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Enzo
Enzo 2023-4-29
@Image Analyst as @Stephen23 spotted in no time, my issue was way more stupid than one could thought. I was doing it wrong starting from the very first line. Sorry to wasted your time, but thanks for your efforts

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