Pandas rank by column value [duplicate]

Question

I have a dataframe that has auction IDs and bid prices. The dataframe is sorted by auction id (ascending) and bid price (descending):

Auction_ID    Bid_Price 123           9 123           7 123           6 123           2 124           3 124           2 124           1 125           1 

I'd like to add a column called 'Auction_Rank' that ranks auction id's by bid prices:

Auction_ID    Bid_Price    Auction_Rank 123           9            1 123           7            2 123           6            3 123           2            4 124           3            1 124           2            2 124           1            3 125           1            1 

Answer 1

Here's one way to do it in Pandas-way

You could groupby on Auction_ID and take rank() on Bid_Price with ascending=False

In [68]: df['Auction_Rank'] = df.groupby('Auction_ID')['Bid_Price'].rank(ascending=False)  In [69]: df Out[69]:    Auction_ID  Bid_Price  Auction_Rank 0         123          9             1 1         123          7             2 2         123          6             3 3         123          2             4 4         124          3             1 5         124          2             2 6         124          1             3 7         125          1             1