What is rank in Python?

Question

I've curious about rank in Python. How did the output arrive as printed below? What did rank do the data?

Input obj = pd.Series([7,-5,7,4,2,0,4])

Output:

    print(obj)
    0    7
    1   -5
    2    7
    3    4
    4    2
    5    0
    6    4

Rank

    print(obj.rank())
    0    6.5
    1    1.0
    2    6.5
    3    4.5
    4    3.0
    5    2.0
    6    4.5

Answer 1

According to the official Pandas Documentation, it does the following:

Compute numerical data ranks (1 through n) along axis. Equal values are assigned a rank that is the average of the ranks of those values

This means that essencially all values get assigned a "highscore". The Value 7 is the highest and therefore gets the highest ranking but since the value 7 is there twice, it both gets the highscore 7 AND 6. But since the value 7 can not have 2 different "highscores", it gets assigned the average of both rankings. (6+7)/2 is 6.5 -> that is the ranking of the data Value 7. other values are more straight forward, for example -5 is the lowest and therefore gets the worst rank.