Finding median of large set of numbers too big to fit into memory

Question

I was asked this question in an interview recently.

There are N numbers, too many to fit into memory. They are split across k database tables (unsorted), each of whi

Answer 1

Another way to look at this is to go back to the definition of "median." Authors vary in their language, but basically the median is the value which splits a probability distribution into two equal parts.

So instead of spending a lot of effort sorting enormous data sets, estimate the distribution and find the middle. As noted above for some distributions the median equals the mean, which is quick and easy to compute. Also, if an exact answer isn't necessary you can use the empirical relationship: mean - mode = 3 * (mean - median).