Simple formula to calculation of the h-index

h-index.py

def hIndex(citations):
    """
    https://github.com/kamyu104/LeetCode/blob/master/Python/h-index.py
    :type citations: List[int]
    :rtype: int
    
    # Given an array of citations (each citation is a non-negative integer)
    # of a researcher, write a function to compute the researcher's h-index.
    #
    # According to the definition of h-index on Wikipedia: 
    # "A scientist has index h if h of his/her N papers have
    # at least h citations each, and the other N − h papers have
    # no more than h citations each."
    #
    # For example, given citations = [3, 0, 6, 1, 5], 
    # which means the researcher has 5 papers in total
    # and each of them had received 3, 0, 6, 1, 5 citations respectively. 
    # Since the researcher has 3 papers with at least 3 citations each and 
    # the remaining two with no more than 3 citations each, his h-index is 3.
    #
    # Note: If there are several possible values for h, the maximum one is taken as the h-index.
    """
    return sum(x >= i + 1 for i, x in enumerate(sorted(  list(citations), reverse=True)))

See:https://en.wikipedia.org/wiki/H-index#Calculation.

R implementation: https://stackoverflow.com/a/56245343/2268280