average sections of matrix
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Hi there, I am trying to average sections of a matrix at a time. The matrix is 31x109. Initially I am trying to build another matrix from the average of the first 25 elements increments in the first row, then the second 25(beginning from the the last element in the previous average); this will later be applied to all rows. My current attempt is
for f = 1:[1:25:108]; Ave_PpIX(f,:) = PpIX_Dose_Matrix(1,1:f); end
ave_PpIX = mean(Ave_PpIX);
Am idea of the matrix is: [ave(1-25) ave(13-38) ave(25-50)...]
If anyone has had any previous experience doing this I would really appreciate any help.
Thnaks Luke
1 个评论
Jan
2018-7-12
Why 108 in the loop, not 109? What should happen with the last chunk, which has less then 25 elements?
1:[a:b:c] is the same as 1:a.
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Star Strider
2018-7-12
I am not certain that I understand the result you want.
Try this:
M = rand(31, 109); % Original Matrix
Cols = [ones(1, fix(size(M,2)/25))*25 rem(size(M,2),25)]; % Create Column Sub-Sections
C = mat2cell(M, size(M,1), Cols); % Cell Array Of Sub-Sections
Cmean = cellfun(@(x)mean(x,2), C, 'Uni',0); % Row Means For Each Section
Mmean = cell2mat(Cmean); % Convert To Double Matrix Of Row Mean Vectors For Each Sub-Section
9 个评论
Luke McLellan
2018-7-13
Star Strider
2018-7-13
My pleasure.
‘I have just realised ... that the matrix values should be [1-25 13-38 25-50...]...’
You can easily implement this in my code by changing the ‘Cols’ vector, and segment the matrix as many times as necessary to get all the segments you want.
For example one line would be:
Cols1 = [25 25 ...];
C1 = mat2cell(M, size(M,1), Cols1);
and a second call:
Cols2 = [12 26 ...]; % The Second Segment Will Be Columns 13-38
C2 = mat2cell(M, size(M,1), Cols2);
The code becomes a bit more complicated with the additional segmentation steps. It is still relatively straightforward and efficient. The column dimensions in the ‘Cols1’ and ‘Cols2’ vectors each have to total the column size (dimension 2) of your matrix, 109 here.
Luke McLellan
2018-7-16
Star Strider
2018-7-16
As always, my pleasure.
If you only want columns 13-38, this works:
Cols2 = [12 26 size(M,2)-(12+26)];
The second segment of the mat2cell result is the one you want.
To be certain ‘Cols2’ (or any other segmentation vector) will work in mat2cell, ‘sum(Cols2)’ has to equal ‘size(M,2)’. (All elements must of course be integers.)
Luke McLellan
2018-7-16
Luke McLellan
2018-7-16
Star Strider
2018-7-16
The 13-38 segment is 26 elements, so to repeat 3 consecutive segments, ‘Cols2’ becomes:
Cols2 = [12 26 26 26 size(M,2)-(26*3+12)];
that becomes ‘[12 26 26 26 19]’, in mat2cell creating segments from columns 1-12. 13-38, 39-64, 65-90, and 91-109. So here, use segments 2, 3, and 4 out of the 5 segments created.
Luke McLellan
2018-7-17
Star Strider
2018-7-17
Thank you!
更多回答（1 个）
PpIX_Dose_Matrix = rand(31, 109);
n = size(PpIX_Dose_Matrix, 2);
k = 0;
for f = 1:24:n
k = k + 1;
Ave_PpIX(k) = mean(PpIX_Dose_Matrix(1, f:f+24));
end
This can fail, when f+25 is outside the existing range. A test with if can catch this:
if f+25 <= n
...
3 个评论
Luke McLellan
2018-7-13
编辑：Luke McLellan
2018-7-13
Jan
2018-7-13
for f = 1:12:n
k = k + 1;
Ave_PpIX(k) = mean(PpIX_Dose_Matrix(1, f:f+24));
end
Luke McLellan
2018-7-16
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