MATLAB: How to get average of multiple rows and subtract from one group of average to another

matlab function

Hello,

I have a big file with multiple rows and columns. I need to get the average of every 30 rows. for example from row 1 to 30, 31 to 60, 61 to 90 and so on until the end of the rows. Can anyone help me with this? any kinds of help will be really appriciated.

Best Answer

M = your matrix with 10039 rows and 64 columns
N = 30;
whole_blocks = floor(size(M,1)/N);
leftover = size(M,1) - whole_blocks * N;
last_whole = whole_blocks * N;
whole_mean = reshape( mean(reshape(M(1:last_whole, N, [])), 2), whole_blocks, [] );
extra_mean = mean(M(last_whole+1:end, :),1);
overall_mean = [whole_mean; extra_mean];

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MATLAB: How to find the mean after every n columns

This could be done with a simple for-loop or a slightly trickier reshape:

% Simple data
x = repmat(1:16,3,1)
nrows = 4; % rows to mean
meanby4 = squeeze(nanmean(reshape(x.',nrows,size(x,2)./nrows,[]))).'

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 >>588845/48
 ans = 
      12267.604

The number of rows is not divisible by 48. What are you planning to do with the last few rows?

Assuming you have a number of rows divisible by 48, the easiest is to reshape the matrix into 48 rows, and take the mean along the rows.

m = reshape(1:5888450, 588845, 10);   %demo data, replace by your own matrix
croppedm = m(1 : size(m,1)-mod(size(m, 1), 48), :);  %crop number of rows to multiple of 48
meancroppedm = squeeze(mean(reshape(croppedm, 48, [], size(m, 2)), 1))  %mean along rows

The mean of the last portion:

meancutm = mean(m(size(m, 1)-mod(size(m, 1),48) : end, :), 1)

The two combined

mean48 = [meancroppedm; meancutm]

Best Answer

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MATLAB: How to find the mean after every n columns

MATLAB: Calculating the average from a large excel file

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