Python Data Structures and Algorithms

Selection by sorting

Items in a list may undergo statistical enquiries such as finding the mean, median, and mode values. Finding the mean and mode values do not require the list to be ordered. However, to find the median in a list of numbers, the list must first be ordered. Finding the median requires one to find the element in the middle position of the ordered list. But what if we want to find the last-smallest item in the list or the first-smallest item in the list?

To find the ith-smallest number in an unordered list of items, the index of where that item occurs is important to obtain. But because the elements have not been sorted, it is difficult to know whether the element at index 0 in a list is really the first-smallest number.