Efficient summing of parts of an array
4 ビュー (過去 30 日間)
古いコメントを表示
I have a 4D dataset that I'm expressing as a sparse 2D array of 1s and 0s. The 4D data has dimensions NPixHeight by NPixWidth by NBins by NFrames, and as a sparse array has the dimensions NPixHeight*NFrames by NPixWidth*NBins.
As part of my pre processing of I want to compress the 2D array by summing along the F dimension in groups, the size of the group is defined by nExps in the below code. To realise this I create and transform matrix T that after multiplication with the original array outputs a NPixHeight*nExps by NPixWidth*NBins array.
This last step is pretty slow for our planned application and I was hoping someone might be able to point me in the right direction to speed it up.
Here's an excerpt from the code
%% Data Reshape
% number of exposures for macro time
nExps = NFrames/macroFrames;
% generates sparse array of counts Ypix*NFrames by Xpix*Bins where
% NFrames is limited by macrotime
yNew = y+(f-1).*NPixHeight;
xNew = x+(b-1).*NPixWidth;
SpCounts = sparse(yNew,xNew,1,NPixHeight*NFrames,NPixWidth*NBins); % SLOW
% transform matrix that sums a number frames set by macro time
T = repmat(speye(NPixHeight,NPixHeight),1,macroFrames);
TCell = repmat({T}, 1, nExps);
clearvars T
T = blkdiag(TCell{:});
% multiplication and reshaping to output
% 4D array of Y x X x Bins x NumberMacroExposures
camData.counts = sparse(size(SpCounts,2),size(T,1));
camData.counts = full(T*SpCounts).'; % SLOW
camData.counts = reshape(camData.counts,NPixWidth*NBins,NPixHeight,nExps);
camData.counts = reshape(pagetranspose(camData.counts),NPixHeight,NPixWidth,NBins,nExps);
(I know the double reshape is awkard but its not enough of a bottleneck to bother fixing)
採用された回答
Matt J
2023 年 7 月 24 日
I would recomend that you maintain the 4D array in ndSparse form instead,
at which point you can do,
temp = reshape(yourArray,[],NFrames)*kron(speye(nExps),ones(macroFrames,1));
result=reshape(temp,NPixHeight, NPixWidth , NBins, []);
その他の回答 (0 件)
参考
カテゴリ
Help Center および File Exchange で Logical についてさらに検索
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!