how to average specific rows of all columns?

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laxminarayana pasupuleti 2017-6-10

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回答： J Yadav 2019-1-16

i am having 100x32 matrix in my data set. i would like to average 20 rows of all columns, like first 20rows average, next 20 and so..on...

can any one help in this problem.

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the cyclist 2017-6-10

Would the output be, in your example, a 5x32 matrix?

laxminarayana pasupuleti 2017-6-12

yes

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Answer 1

the cyclist 2017-6-10

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编辑：the cyclist 2017-6-10

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If I understand your question correctly, you can use the movmean command:

% Some made-up data
A = rand(100,32);
N = 20;
movingAverageA = movmean(A,[(N-1) 0]); % Trailing average of N rows
output = movingAverageA(N:N:end,:);

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Image Analyst 2017-6-12

Did you get it working? You've accepted this answer so I assume so.

laxminarayana pasupuleti 2017-6-12

in my version its not woking..so i am trying latest version...

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Answer 2

J Yadav 2019-1-16

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to take a moving average of 1 to 20 rows, then 21-40 rows, then 41-60 rows etc.

of a data matrix with n rows and m columns.

you may also try:

for i=1:(n/20) % given that n is a multpile of 20 or your choice of no. of rows to average.
    a=(i-1)*20+1;
    b=(i-1)*20+20;
    meandata(i,:) = mean(data(a:b,:),1);
end

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Answer 3

Image Analyst 2017-6-10

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编辑：Image Analyst 2017-6-12

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The first index are the rows. For example to average only the first 20 rows

columnMeans = mean(data([1:20], :), 1);

Or to average rows 34, 23, and 194, do

rowsToAverage = [34, 23, 194];
columnMeans = mean(data(rowsToAverage, :), 1);

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laxminarayana pasupuleti 2017-6-12

this is not working

Image Analyst 2017-6-12

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This seems to work:

data = randi(9, 100, 32) % Sample 100x32 data
columnMeans = [
  mean(data([1:20], :), 1);
  mean(data([21:40], :), 1);
  mean(data([41:60], :), 1);
  mean(data([61:80], :), 1);
  mean(data([81:100], :), 1)]

Is that what you want?

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