How do I find averages of certain values in a matrix.

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Lakyn 2016-8-22

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https://ww2.mathworks.cn/matlabcentral/answers/300518-how-do-i-find-averages-of-certain-values-in-a-matrix

评论： Walter Roberson 2016-8-23

Hi all!

So basically I have a 76x76 matrix, but I want to find the average for the values for the corresponding pairs, e.g. 1x2 and 2x1, 22x37 and 37x22, 6x58 and 58x6 etc, from 1x2 and 2x1 all the way to 75x76 and 76x75 (excluding repeated numbers like 1x1). Is there a way for me to do this and put it into like a table?

Thank you!

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Azzi Abdelmalek 2016-8-22

What is the size of the expected result?

Lakyn 2016-8-22

编辑：Lakyn 2016-8-22

It will be 1+2+3...+75, so 2850!

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采纳的回答

Walter Roberson 2016-8-22

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https://ww2.mathworks.cn/matlabcentral/answers/300518-how-do-i-find-averages-of-certain-values-in-a-matrix#answer_232495

在 MATLAB Online 中打开

What does 22x37 denote here? Is that YourMatrix(22,37) Or is it all sub-matrices that are 22 rows and 37 columns?

Guessing on what you want:

triu( (YourMatrix + YourMatrix.') / 2, 1)

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Lakyn 2016-8-23

Hi,

oh wow thanks so much! I just tried them all. I couldn't get the second one to run though, it says there an error in the last line (output_vector = temp(mask);).

Also, I don't really understand the output of the third way, it doesn't really give any results!

Walter Roberson 2016-8-23

在 MATLAB Online 中打开

temp = (YourMatrix + YourMatrix.') / 2;
mask = triu( true(size(temp)), 1 );
output_vector = temp(mask);

The last of them produces a cell array output; see http://www.mathworks.com/help/matlab/cell-arrays.html

output_cell{1} is the first diagonal as a vector, output_cell{2} is the second diagonal as a vector, and so on. The diagonals are the pairs whose indices add up to the same value -- so for example T(2,75), T(3,74), T(4,73), T(5,72) and so on. You have not really said what you want the table to look like.

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