Problem in my for loop to find maximum y value

Question

Ismail Qeshta 2017-11-11

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编辑： Jan 2017-11-12

Hi, my for loop keeps repeating the same third value for the maximum index value. Can anyone please check it for me? the full code is:

for k = 1:3
    Driftt  = sprintf('Drift%d.out', k);
    Reactt  = sprintf('React%d.out', k);
    matDrift = importdata(fullfile(Driftt));
    matReact = importdata(fullfile(Reactt));
    x= matDrift(:,2);
    y= -sum(matReact(:,2:11),2);
    plot(x,y)
    hold on;
    %
    sort = zeros(N,2);
    for i=1:N
        [valy,idx] = max(y);
        sort(i,:) = [x(idx,1),valy];
        hold on;
    end
end

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Ismail Qeshta 2017-11-11

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The problem is in this part:

sort = zeros(N,2);
    for i=1:N
    [valy,idx] = max(y);
    sort(i,:) = [x(idx,1),valy];
    hold on;
    end
  end

Ismail Qeshta 2017-11-11

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files = dir('*.out') ;
N = length(files) ;
sorted = zeros(N,2) ;
for i = 1:N
    data = importdata(files(i).name) ;
    [val,idx] = max(data(:,2)) ;
    sorted(i,:) = [data(idx,1),val] ;
end

This code is similar to the one I am using. This code works well, but with the x and y data in the same file. In my case, I am plotting data from two separate files.

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Answer 1

Jan 2017-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/366462-problem-in-my-for-loop-to-find-maximum-y-value#answer_290582

编辑：Jan 2017-11-11

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The code contains several problems:

1. fullfile(Driftt) does not do anything. Define the directory in addition:

Folder = cd;
...
   matDrift     = importdata(fullfile(Folder, Driftt));

2. Do not use "sort" as name of a variable, because this shadows the important function with the same name. This is not an error directly, but trying to use the function|sort()| afterwards produces unexpected behavior.

3. What is the value of "N"?

Perhaps you want:

    sorted = zeros(N,2);
    for i = 1:N
      [valy, idx] = max(y(i, :));  % or y(:, i)?
      sorted(i,:) = [x(idx,1), valy];
      % hold on;  Completely useless here, remove it
    end

hold set the 'NextPlot' property of the current axes such that following plot commands do not remove existing line objects. But you are nor drawing here.

You could do this without a loop also:

[valy, idx] = max(y, [], 2);  % or max(y, [], 1) ?
sorted      = [x(idx, 1), valy];

Perhaps you have to modify the dimensions for the concatenation.

4. The variable "sort" (renamed to "sorted" in my code) is overwritten. Perhaps you want:

sorted = cell(1, 3);
...
[valy, idx] = max(y, [], 2);  % or max(y, [], 1) ?
sorted{k}   = [x(idx, 1), valy];

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Ismail Qeshta 2017-11-12

编辑：Ismail Qeshta 2017-11-12

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Hi Jan. Great. Thank you very much. It worked for x values. But for y values, I need to take the summation of columns (from 2 to 11) at each row. I am not sure where I shall put the code:

-sum(ReactData(:,2:11),2)

Ismail Qeshta 2017-11-12

编辑：Ismail Qeshta 2017-11-12

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All Good. I could figure it out. Thanks Jan for all your help. You have been awesome.

The code now is:

DriftFiles = dir('Drift*.out');
ReactFiles = dir('React*.out');
N          = length(DriftFiles);
sorted     = zeros(N, 2);
for k = 1:N
  DriftData   = importdata(DriftFiles(k).name) ;
  ReactData   = importdata(ReactFiles(k).name) ;
  Reactt = -sum(ReactData(:,2:11),2);
  Driftt= DriftData(:,2);
  [val, idx]  = max(Reactt);
  sorted(k,:) = [Driftt(idx, 1), val];
end

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Answer 2

Birdman 2017-11-11

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https://ww2.mathworks.cn/matlabcentral/answers/366462-problem-in-my-for-loop-to-find-maximum-y-value#answer_290580

编辑：Birdman 2017-11-11

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Because you keep overwriting Driftt and Reactt variables in the first for loop. When k=3, Driftt and Reactt arrays take their last shape and therefore you always see same maximum value.

    Driftt  = sprintf('Drift%d.out', k);
    Reactt  = sprintf('React%d.out', k);

This part causes the problem. At last when k=3, Driftt is equal to Drift3.out file and same for the other. Change this. You might need indexing.

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Ismail Qeshta 2017-11-11

Thank you for the suggestion. I tried to remove the first for loop, but the problem is still occurring.

Jan 2017-11-11

编辑：Jan 2017-11-11

No, Driftt nor Reactt are overwritten intentionally, because they are changing file names. There is no problem if the file name is "Drift3.out" for k=3.

The variable "sort" is overwritten repeatedly, so this might be the problem.

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