For loop with different length

Question

Uerm 2019-11-24

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/492944-for-loop-with-different-length

评论： Uerm 2019-11-25

Hello,

I have a 1x10 cell (Var), where each cell is a 50*20000*A 3D array. I am trying to run the following code:

for k = 1:N
    for j = 1:50
        for i = 1:10
            test{i} = mean(Var{i}(j,:,k));
            test2{i} = std(Var{i}(j,:,k));
        end
    end
end

However, as apparent the number N will be different as A changes for each cell. How can I compute this with different N?

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Answer 1

Roofus Milton 2019-11-25

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See last section of code. I used a counter variable which is incremented.

rows = 50;
columns = 20000;
randRange = [10, 50];
% create the cell array
data = cell(1, 10);

% loop over cell array and create matricies with varying size of third
% dimension
for p = 1:length(data)
    data{p} = rand(rows, columns, randi(randRange));
end

% get the size of each matrix
dimensions = cell2mat(cellfun(@size, data, 'UniformOutput', false)');

% calculate how many rows will be needed
totalRows = sum(dimensions(:, 1) .* dimensions(:, 3));

% preallocate the output matrix
output = zeros(totalRows, columns);

% initialize the counter variable
counter = 1;
% loop over cell
for i = 1:length(data)
    
    % loop over rows
    for j = 1:dimensions(i, 1)
        
        % loop over third dimension
        for k = 1:dimensions(i, 3)
            
            % assign the data
            output(counter, :) = data{i}(j, :, k);
            
            % increment the counter
            counter = counter + 1;
            
        end
    end
end

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Roofus Milton 2019-11-25

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This is really a different question. m, s, X, and Y are not defined in your code or mine. I believe the below accoplishes what you are getting at.

Replace the las two sections of code above with these snippets.

% preallocate the output matrix
outputData = zeros(totalRows, columns);

% create a cell array of functions you want to calculate
f = {@mean, @std};
% preallocate the stats matrix
outputStats = zeros(totalRows, length(f));

% initialize the counter variable
counter = 1;
% loop over cell
for i = 1:length(data)
    
    % loop over rows
    for j = 1:dimensions(i, 1)
        
        % loop over third dimension
        for k = 1:dimensions(i, 3)
            
            % assign the data
            outputData(counter, :) = data{i}(j, :, k);
            
            % loop over the stats you want to calculate
            for g = 1:length(f)
                outputStats(counter, g) = f{g}(outputData(counter, :));
            end
            
            % increment the counter
            counter = counter + 1;
            
        end
    end
end