How Does Pandas' `rank()` Function Implement Dense Ranking?

DENSE RANK function in Pandas

The DENSE_RANK() function in Pandas is used to calculate the rank of each row in the data frame, assigning the same rank to the same value. To implement this functionality we can use the pd.Series.rank method and set method='dense'.

Let us consider the following data frame:

<code>Year  Value
2012  10
2013  20
2013  25
2014  30</code>

To create an additional column "Rank" containing dense ranking, we can use the following code:

<code>df['Rank'] = df.Year.rank(method='dense').astype(int)</code>

The resulting data frame is as follows:

<code>    Year  Value  Rank
0  2012     10     1
1  2013     20     2
2  2013     25     2
3  2014     30     3</code>

In this output, the duplicate values ​​from 2013 are all assigned a rank of 2, demonstrating the behavior of dense ranking.

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