calculate the mean of several columns

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Sobhan
Sobhan 2012-4-4
评论： Walter Roberson 2015-12-2
Hi all, I am new to Matlab and I am struggling with this problem. I have a matrix with 112 columns and 100 rows. How can I calculate the mean of column 1-7 , 8-14, 15-21,...., 106-112 and put the a new matrix with 16 columns and 100 rows. I appreciate your help Sobhan
  2 个评论
Andrei Bobrov
Andrei Bobrov 2012-4-5
eg
A = rand(100,112);
fun = @(block_struct)mean(block_struct.data,2);
out = blockproc(A,[100,7],fun);

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采纳的回答

Wayne King
Wayne King 2012-4-4
One way is simply with a for loop
A = randn(100,112);
for nn = 0:15
B(:,nn+1) = mean(A(:,nn*7+1:(nn+1)*7),2);
end
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Oleg Komarov
Oleg Komarov 2012-4-4
I bet this is more efficient than the one liner and definitely more readable.

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更多回答（3 个）

Oleg Komarov
Oleg Komarov 2012-4-4
A = rand(100,112);
B = reshape(mean(reshape(A.',7,[])),16,100).';
% Check
isequal(mean(A(2,8:14)),B(2,2))
Thomas
Thomas 2012-4-4
You could reshape your matrix with 7 columns becoming 1 in the new matrix and taking the mean of each column
Eg.:
c=rand(4) % 4x4 matrix
d=reshape(c,[],2) % take two colm and form 1 total 2
p=mean(d) % mean of each columns
In your case
c=rand(100,112) % 4x4 matrix
d=mean(reshape(c,7,[])) % form 1600 columsns
final_out=(reshape(d,16,100)) % mean of each columns
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Oleg Komarov
Oleg Komarov 2012-4-4
Now, your mean is across the first 7 rows (first column). You have to transpose and re-transpose back. Honestly, in this cases I think Waynes solution is best in terms or readability and performance.

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Sobhan
Sobhan 2012-4-5
Dear all, Waynes` solution worked like a charm. You are awesome. Thanks a lot for your nice suggestions :)

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