Thank you for the help, what you say makes sense. In this application, I need to access the data both by rows and by columns in different loops. What is the best way to optimize this? Ideally I'd want to specify a different chunkshape for each loop, but I guess that would require storing two copies of the data (which is not impossible, if that's the only way). Basically I want to divide each row of data by the mean of that row, and then perform a calculation on each column. Glenn
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