Printing Results out of a for Loop

Question

Ammar Taha 2019-6-27

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https://ww2.mathworks.cn/matlabcentral/answers/469152-printing-results-out-of-a-for-loop

评论： Ruger28 2019-6-27

I have Written a Small Function that Returns the Absolute Difference Between the Max and Min Elements of Each Row in a Matrix and Assigns the Results to the output "rows_diff" as Row Vector and Also Gets the Diff. Between the Max and Min of Whole Matrix in "tot_diff"

All what I want to Know is How to Print Out the Results of the for Loop Returning them in "rows_diff" as row vector not just the Last Result as the Case with this Version of the Function:-

function [rows_diff, tot_diff] = minimax(M)

a = size(M,1);

for i = 1:a

rows_diff = abs(max(M(i,:)) - min(M(i,:)));

end

tot_diff = max(M(:)) - min(M(:));

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Stephen23 2019-6-27

编辑：Stephen23 2019-6-27

在 MATLAB Online 中打开

Note that avoiding the loop gives simpler, more efficient code:

>> M = magic(5) % fake data.
M =
   17   24    1    8   15
   23    5    7   14   16
    4    6   13   20   22
   10   12   19   21    3
   11   18   25    2    9
>> minimax(M) % function with loop (following Ruger28's bugfix).
ans =
   23   18   18   18   23
>> max(M,[],2) - min(M,[],2) % no loop required, more efficient.
ans =
   23
   18
   18
   18
   23

Ammar Taha 2019-6-27

Thanks Again Stephen, but I was doing an Assigment for a Course and it was Required to use for Loop Specificaly.

I have read this before and I will try to Aviod Looping in Future.

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Answer 1

Ruger28 2019-6-27

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rows_diff = abs(max(M(i,:)) - min(M(i,:)));

This overwrites the value of rows_diff each time. This is ok if you just want to print it out, but to store it (which seems like you want to) you need:

rows_diff(i) = abs(max(M(i,:)) - min(M(i,:)));

to print this value, in your loop place a fprintf

fprintf('Value of rows_diff = %f\n',rows_diff(i))

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Stephen23 2019-6-27

编辑：Stephen23 2019-6-27

Remember to preallocate any arrays before the loop:

https://www.mathworks.com/help/matlab/matlab_prog/preallocating-arrays.html

Ammar Taha 2019-6-27

Thanks alot Stephen Matlab has Pointed this Out and I Made it :)

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Answer 2

Alex Mcaulley 2019-6-27

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/469152-printing-results-out-of-a-for-loop#answer_381036

在 MATLAB Online 中打开

You can also implement the function in a simpler and efficient way:

function [rows_diff, tot_diff] = minimax(M)
    rows_diff = arrayfun(@(i) abs(max(M(i,:)) - min(M(i,:))),1:size(M,1))';
    tot_diff = max(M(:)) - min(M(:));
end