How compute the percentile in PySpark dataframe for each key?

Question

I have a PySpark dataframe consists of three columns x, y, z.

X may have multiple rows in this dataframe. How can I compute the percentile of each key in x separately?

+------+---------+------+
|  Name|     Role|Salary|
+------+---------+------+
|   bob|Developer|125000|
|  mark|Developer|108000|
|  carl|   Tester| 70000|
|  carl|Developer|185000|
|  carl|   Tester| 65000|
| roman|   Tester| 82000|
| simon|Developer| 98000|
|  eric|Developer|144000|
|carlos|   Tester| 75000|
| henry|Developer|110000|
+------+---------+------+

The output needed:

+------+---------+------+---------+
|  Name|     Role|Salary|      50%|
+------+---------+------+---------+
|   bob|Developer|125000|117500.0 |
|  mark|Developer|108000|117500.0 |
|  carl|   Tester| 70000|72500.0  |
|  carl|Developer|185000|117500.0 |
|  carl|   Tester| 65000|72500.0  |
| roman|   Tester| 82000|72500.0  |
| simon|Developer| 98000|117500.0 |
|  eric|Developer|144000|117500.0 |
|carlos|   Tester| 75000|72500.0  |
| henry|Developer|110000|117500.0 |
+------+---------+------+---------+

Answer 1

Try groupby + F.expr:

import pyspark.sql.functions as F

df1 = df.groupby('Role').agg(F.expr('percentile(Salary, array(0.25))')[0].alias('%25'),
                             F.expr('percentile(Salary, array(0.50))')[0].alias('%50'),
                             F.expr('percentile(Salary, array(0.75))')[0].alias('%75'))
df1.show()

Output:

+---------+--------+--------+--------+
|     Role|     %25|     %50|     %75|
+---------+--------+--------+--------+
|   Tester| 68750.0| 72500.0| 76750.0|
|Developer|108500.0|117500.0|139250.0|
+---------+--------+--------+--------+

Now you might join df1 with the original dataframe:

df.join(df1, on='Role', how='left').show()

Output:

+---------+------+------+--------+--------+--------+
|     Role|  Name|Salary|     %25|     %50|     %75|
+---------+------+------+--------+--------+--------+
|   Tester|  carl| 70000| 68750.0| 72500.0| 76750.0|
|   Tester|  carl| 65000| 68750.0| 72500.0| 76750.0|
|   Tester| roman| 82000| 68750.0| 72500.0| 76750.0|
|   Tester|carlos| 75000| 68750.0| 72500.0| 76750.0|
|Developer|   bob|125000|108500.0|117500.0|139250.0|
|Developer|  mark|108000|108500.0|117500.0|139250.0|
|Developer|  carl|185000|108500.0|117500.0|139250.0|
|Developer| simon| 98000|108500.0|117500.0|139250.0|
|Developer|  eric|144000|108500.0|117500.0|139250.0|
|Developer| henry|110000|108500.0|117500.0|139250.0|
+---------+------+------+--------+--------+--------+