How can I create another matrix with the sum of every 30 rows in a 14,400 by 11 matrix?
6 views (last 30 days)
Show older comments
I have a matrix with 11 columns of daily data for 40 years (14,400 days) and need the sum of every 30 days to be calculated. After looking around a lot I decided I'd ask on here. Thanks in advance for the help!
0 Comments
Accepted Answer
More Answers (5)
Image Analyst
on 13 Jun 2014
Did you try the brute force approach? It's pretty simple and intuitive and fast:
m = randi(9, [14400, 11]);
otuputRow = 1;
for row = 1 : 30 : size(m, 1)
theSums(otuputRow, :) = sum(m(row:row+29,:));
otuputRow = otuputRow + 1;
end
theSums
0 Comments
Matt J
on 13 Jun 2014
If the 30-day blocks to be summed are tiled, you can also do
result = downsampn(yourMatrix,[30,1])*30;
where downsampn is given by,
function M=downsampn(M,bindims)
%DOWNSAMPN - simple tool for downsampling n-dimensional nonsparse arrays
%
% M=downsampn(M,bindims)
%
%in:
%
% M: an array
% bindims: a vector of integer binning dimensions
%
%out:
%
% M: the downsized array
nn=length(bindims);
[sz{1:nn}]=size(M); %M is the original array
sz=[sz{:}];
newdims=sz./bindims;
args=num2cell([bindims;newdims]);
M=reshape(M,args{:});
for ii=1:nn
M=mean(M,2*ii-1);
end
M=reshape(M,newdims);
1 Comment
Cedric
on 13 Jun 2014
I don't think that we can beat this one. I expected Andrei's solution to be faster, but it seems that dealing with pages makes it slower than iterating over "bindims"..
Cedric
on 13 Jun 2014
Edited: Cedric
on 13 Jun 2014
Here are a couple additional ways, if you need a sum for each block of 30 days (not a "moving" sum), assuming that your original matrix is named M:
Base on accumarray
M_aggregated = zeros( size(M,1)/30, size(M,2) ) ;
blockId = zeros( size(M,1), 1 ) ;
blockId(1:30:end) = 1 ;
blockId = cumsum( blockId ) ;
for cId = 1 : size(M,2)
M_aggregated(:,cId) = accumarray( blockId, M(:,cId) ) ;
end
Based on matrix product
% - Build aggregation matrix.
aggr = repmat( {ones(1,30)}, size(M,1)/30, 1 ) ;
aggr = blkdiag( aggr{:} ) ;
% - Aggregate data.
M_aggregated = aggr * M ;
0 Comments
See Also
Categories
Find more on Logical in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!