CODEWITHSUNDEEP
pythonapache-sparkpysparkapache-spark-sqlwindow-functions
Grevioos
Grevioos

Reputation: 405

Pyspark: Rank() over column and index?

I am having some troubles with window functions. I could not really find any example that would cover scenarios where the order matters. What I want to do, is to rank over ColumnA, taking SortOrder(and their first occurrence) into account. So all of the B would get value 1, A 2 and C 3. Can I achieve it with the rank function? I cannot simply order by those two columns.

example = example.withColumn("rank", F.rank().over(Window.orderBy('ColumnA')))

This one would not work either, since the order would be lost.

from pyspark.sql.types import StructType, StructField, StringType, IntegerType
import pyspark.sql.functions as F
from pyspark.sql.window import Window

data = [("B", "BA", 1),
        ("B", "BB", 2),
        ("B", "BC", 3),
        ("A", "AA", 4),
        ("A", "AB", 5),
        ("C", "CA", 6),
        ("A", "AC", 7)]

cols = ['ColumnA', 'ColumnB', 'SortOrder']

schema = StructType([StructField('ColumnA', StringType(), True),
                     StructField('ColumnB', StringType(), True),
                     StructField('SortOrder', IntegerType(), True)])

rdd = sc.parallelize(data)
example = spark.createDataFrame(rdd, schema)

?
example = example.withColumn("rank", F.rank().over(Window.orderBy('SortOrder', 'ColumnA')))

Upvotes: 0

Views: 2599

Answers (1)

mck
mck

Reputation: 42422

Get the minimum SortOrder for each ColumnA value, then get the rank, and join it back to the original dataframe.

example2 = example.join(
    example.groupBy('ColumnA')
           .min('SortOrder')
           .select('ColumnA',
                   F.rank().over(Window.orderBy('min(SortOrder)')).alias('rank')
                  ),
    on = 'ColumnA'
).orderBy('SortOrder')

example2.show()
+-------+-------+---------+----+
|ColumnA|ColumnB|SortOrder|rank|
+-------+-------+---------+----+
|      B|     BA|        1|   1|
|      B|     BB|        2|   1|
|      B|     BC|        3|   1|
|      A|     AA|        4|   2|
|      A|     AB|        5|   2|
|      C|     CA|        6|   3|
|      A|     AC|        7|   2|
+-------+-------+---------+----+

Upvotes: 1

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