How to take the average of the columns of a matrix and insert into another matrix

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Feliciano Döring 2018-7-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408443-how-to-take-the-average-of-the-columns-of-a-matrix-and-insert-into-another-matrix

编辑： Feliciano Döring 2018-7-3

file.txt

I have a piece of code that reads a .txt file with several matrices and sorts them into cell arrays. Each of the matrices has always three columns with varying rows. My question would be how i can take the average of each column from these matrices separately and put it into another matrix with these averages, so that it would be a new matrix containing 3 columns, each column with the average of the column of the original matrix, and with the number of rows like the number of matrices on the .txt file. Here the code that reads the .txt file and indexed is the .txt file.

filepath = '/Users/...';
fileID = fopen(filepath);
nGroups = 0;
stationGroups = cell(0,1);
while true
    nStations = fgets(fileID);
    if ~ischar(nStations)
        break;
    end
    nGroups = nGroups + 1;
    nStations = str2num(nStations);
    stationMatrix = zeros(nStations,3);
    for currentStation = 1:nStations
        fprintf('Loading station %d of station group %d: ', ...
            currentStation, nGroups);
        testStation = fgets(fileID);
        if ~ischar(testStation)
            error('Error - file ended too early!');
        end
        testStation = str2num(testStation);
        if numel(testStation)~=3
            error('Error - Station %d didn''t have three values!', ...
                currentStation);
        end
        fprintf('%.2f ',testStation);
        fprintf('\n');
        stationMatrix(currentStation,:) = testStation;
    end
    stationGroups{end+1} = stationMatrix;
    nGroups = length(stationGroups);
end
fclose(fileID);

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dpb 2018-7-2

Is the attached file the input file being parsed, I guess, and you want the means of the groups within that file as records in a new file or an array in memory?

Feliciano Döring 2018-7-2

The file contains all the matrices and the programs separates all of them in cell arrays. i want the means from the three columns of each matrix separately and to put it on a new cell array. Hope it helps to understand, i didn't quite get your question

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Answer 1

dpb 2018-7-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/408443-how-to-take-the-average-of-the-columns-of-a-matrix-and-insert-into-another-matrix#answer_327185

在 MATLAB Online 中打开

fid=fopen('file.txt');
mn=[];
while ~feof(fid)
  n=fscanf(fid,'%d',1)
  if isempty(n),break,end
  d=cell2mat(textscan(fid,'%f%f%f',n,'collectoutput',1));
  mn=[mn;mean(d)];
end
fid=fclose(fid);

While the above does dynamic reallocation for "growing" the mn array, unless and until the number of rows in the file gets to be quite large the time required is likely not going to be noticeable. If does, then preallocate mn for a large number of rows and increment a counter and fill in; remembering to check for overflow, of course.