Speed Up the for loop

Question

Arun Kumar Singh 2021-9-16

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454369-speed-up-the-for-loop

评论： Arun Kumar Singh 2021-9-17

 for j=1:120000
     disp(j);
     for i=1:7000000
         disp(i);
          if (strcmpi(x(i),y(j)))
           if (T1(i)==W1(j) && DOY2(i)==W2(j))
               if ((T6(i)-0.125<=W3(j))&&(W3(j)<=T6(i)+0.125))
             
             
   fprintf(fileID,'%s \t %6.2f \t %6.2f \t %6.2f \t %6.2f \t %6.4f \t %6.4f\t %6.2f \t %6.2f \t %6.4f \t %6.4f\t %6.2f \t %6.2f \t %6.2f \t %6.2f',cell2mat(y(j)),T1(i),DOY2(i),T6(i),T7(i),T8(i),T9(i),T10(i),W1(j),W2(j),W3(j),W4(j),W5(j),W6(j),W7(j));
 
  fprintf(fileID,'\n');   
  
                end  
           end        
          end
     end
 end

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Arun Kumar Singh 2021-9-16

This loop has to be run for i=1:7000000 into another loop for j=1:120000 times, How to Speed up this loop ?

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Answer 1

Jan 2021-9-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454369-speed-up-the-for-loop#answer_788989

编辑：Jan 2021-9-16

在 MATLAB Online 中打开

Fmt1 = '%6.2f \t %6.4f \t %6.4f\t %6.2f \t %6.2f \t %6.2f \t %6.2f';
Fmt2 = '%s \t %6.2f \t %6.2f \t %6.2f \t %6.2f \t %6.4f \t %6.4f\t %6.2f \t %s\n';
fileID = fopen(FileName, 'W');  % Uppercase!
for j = 1:120000
   W3u  = W3(j) + 0.125;
   W3l  = W3(j) - 0.125;
   % [EDITED] the {j} belongs to y, not to x:
   m    = strcmpi(x, y{j}) & T1 == W1(j) & DOY2 == W2(j) & ...
            W3l <= T6 & T6 <= W3u;
   WStr = sprintf(Fmt1, W1(j), W2(j), W3(j), W4(j), W5(j), W6(j), W7(j));
   for i = 1:7000000
      if m(i)
         fprintf(fileID, Fmt2, ...
             y{j}, T1(i), DOY2(i), T6(i), T7(i), T8(i), T9(i), T10(i), WStr);
      end
   end
end
fclose(fileID);

AS far as I understand, y and x are cell strings. Then cell2mat(y(j)) is a slow version of y{j} .

13 个评论
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Jan 2021-9-16

在 MATLAB Online 中打开

There was a typo in my code. Why do you avoid to answer my question for the sizes?

I've inserted the code in a function and cleaned it up. For the first 1000 elements my code needs 0.4 seconds instead of 24 seconds of the orignal version:

function DOY_Date_Jan(InFile1, InFile2, OutFile)
fid = fopen(InFile1, 'r');
M   = textscan(fid, '%s%f%f%f%f%f%f%f%f%f%f', 'collectoutput', true);
fclose(fid);
x    = M{1, 1};
M1   = M{1, 2};
T1   = M1(:, 1);
T2   = M1(:, 2);
T3   = M1(:, 3);
% T4   = M1(:, 4);
% T5   = M1(:, 5);
T6   = M1(:, 6);
T7   = M1(:, 7);
T8   = M1(:, 8);
T9   = M1(:, 9);
T10  = M1(:, 10);
date = datetime(T1, T2, T3);
DOY2 = day(date, 'dayofyear');
fid1 = fopen(InFile2, 'r');
datacell1 = textscan(fid1,'%s%f%f%f%f%f%f%f', 'collectoutput', true);
fclose(fid);
M2 = datacell1{1,1};
M3 = datacell1{1,2};
y  = M2(:, 1);
W1 = M3(:, 1);
W2 = M3(:, 2);
W3 = M3(:, 3);
W4 = M3(:, 4);
W5 = M3(:, 5);
W6 = M3(:, 6);
W7 = M3(:, 7);
Fmt1 = '%6.2f \t %6.4f \t %6.4f\t %6.2f \t %6.2f \t %6.2f \t %6.2f';
Fmt2 = '%s \t %6.2f \t %6.2f \t %6.2f \t %6.2f \t %6.4f \t %6.4f\t %6.2f \t %s\n';
fid = fopen(OutFile, 'W');  % Uppercase!
tic
yOld = '';
for j = 1:numel(y)
   % Compare all strings only, if y{j} differs from the previous one:
   if ~strcmp(y{j}, yOld)
      yOld = y{j};
      x_yj = strcmpi(x, y{j});
   end
   
   W3u  = W3(j) + 0.125;
   W3l  = W3(j) - 0.125;
   m    = x_yj & T1 == W1(j) & DOY2 == W2(j) & W3l <= T6 & T6 <= W3u;
   WStr = sprintf(Fmt1, W1(j), W2(j), W3(j), W4(j), W5(j), W6(j), W7(j));
   for i = find(m)
      fprintf(fid, Fmt2, ...
         y{j}, T1(i), DOY2(i), T6(i), T7(i), T8(i), T9(i), T10(i), WStr);
   end
end
toc
fclose(fid);
end

I call it with the provided files as:

DOY_Date_Jan('File_i.txt', 'File_j.txt', 'All_Previous_Swarm_A_2.xls')

Some hints:

Do not forget to close files after opening them.
Write one command per line, because this is easier to read.
Hiding numbers in the names of variables is not useful. "T8" is not better than "M1(:, 8)".
Avoid hard-coded limits of loops, but adjust them to the size of the data.
Instead of inserting the file names in the code, provided them as inputs to a function.

Jan 2021-9-17

编辑：Jan 2021-9-17

Sorry, the interface of the forum does not let my type, what I want to. Code formatting should be easy and intuitive, but the editor in this forum is a mess.

Change the line " for i = find(m) " to " for i = find(m).' "

You know, that you can use the debugger to fix such problems also?

Arun Kumar Singh 2021-9-17

Thanks

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Answer 2

Bjorn Gustavsson 2021-9-16

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1454369-speed-up-the-for-loop#answer_788849

在 MATLAB Online 中打开

A couple of suggestions:

0, check the time spent on different lines by running this script with smaller limits on j and i with the profiler running.

1, cut out the disp(i) and disp(j) entirely. In your version you'll have matlab printing some 8.4*10^11 numbers to the command-window. There's no way that your screen-pixels will survive that. (perhaps put something like:

if mod(j,1000)==0
  fprintf('%d:  %s\n',j,datestr(now,'HH:MM:SS'))
end

in to see that it turns over. You can modify the divisor to get more or less frequent updates

)

2, put the '\n' into the first fprintf call - should/might speed things up.

3, combine all conditions into one if-test, they are supposed to shortcut as soon as the TRUE/FALSE is determined - this might speed up or slow down, but ought to be worth a test.

4, instead of calling cell2mat in every fprintf-call do that separately first for all cells in y to create an array of strings, this might speed things up a bit.

HTH