How can I efficiently select the best N items from a vector in different groups?

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Nieves Lopez 2018-12-6

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https://ww2.mathworks.cn/matlabcentral/answers/434291-how-can-i-efficiently-select-the-best-n-items-from-a-vector-in-different-groups

编辑： Nieves Lopez 2018-12-6

I need to select the best (weighted) items from several groups (days), like this

days = [737399 737399 737399 737399 737400 737400 737400];
weights = [0.2 0.6 0.8 0.5 0.5 0.2 0.6];
numBestItemsEachDay = 2;
selectedItems = true(size(weights));
for today = unique(days),
    itemsToday = find(days == today);
    if (length(itemsToday)>numBestItemsEachDay),
        [~,selectedItemsToday] = sort(weights(itemsToday),'descend');
        selectedItems(itemsToday(selectedItemsToday((numBestItemsEachDay+1):end))) = false;
    end;
end;
selectedItems