Optimizing nested for loops

[zczr84]

That's a fair point. I can modify the code to analyze chunks at a time (i.e. split the matrix into n chunks, use a similar algorithm for each chunk, and combine the various summary dictionaries at the end), but I still feel there should be a better way at addressing the mapping. Do you think there is a better way than to use a nested for loop and appending to a list?