Yes, thanks for that point. But in my case, an indexed access is more important than a small decrease in speed. I do not expect you to do my work, but maybe you'd give me a hint on how to do it.Currently I'm getting an iterator and throw the first i-1 elements away to get the i-th one. But I think there has to be a much more elegant solution, depending on how the data is managed internally. I already had a look into that but I'm not sure how to use it correctly.
Isn't this the approach you asked?
This a very helpful hint, thank you. And I may assume that the arrays are filled in sorted order?