PySpark Groupby Explained with Example

Similar to SQL GROUP BY clause, PySpark groupBy() transformation that is used to group rows that have the same values in specified columns into summary rows. It allows you to perform aggregate functions on groups of rows, rather than on individual rows, enabling you to summarize data and generate aggregate statistics.

Related: How to group and aggregate data using Spark and Scala

1. GroupBy() Syntax & Usage

Following is the syntax of the groupby

# Syntax
DataFrame.groupBy(*cols)
#or 
DataFrame.groupby(*cols)

When we perform groupBy() on PySpark Dataframe, it returns GroupedData object which contains below aggregate functions.

Function	Definition
count()	Use groupBy() count() to return the number of rows for each group.
mean()	Returns the mean of values for each group.
max()	Returns the maximum of values for each group.
min()	Returns the minimum of values for each group.
sum()	Returns the total for values for each group.
avg()	Returns the average for values for each group.
agg()	Using groupBy() agg() function, we can calculate more than one aggregate at a time.
pivot()	This function is used to Pivot the DataFrame, which I will not cover in this article as I already have a dedicated article for Pivot & Unpivot DataFrame.

Before we proceed, let’s construct the DataFrame with columns such as “employee_name”, “department”, “state”, “salary”, “age”, and “bonus”.

We will use this PySpark DataFrame to run groupBy() on “department” columns and calculate aggregates like minimum, maximum, average, and total salary for each group using min(), max(), and sum() aggregate functions, respectively.

from pyspark.sql import SparkSession

# Initialize SparkSession
spark = SparkSession.builder \
    .appName("example") \
    .getOrCreate()

# Data
simpleData = [("James","Sales","NY",90000,34,10000),
    ("Michael","Sales","NY",86000,56,20000),
    ("Robert","Sales","CA",81000,30,23000),
    ("Maria","Finance","CA",90000,24,23000),
    ("Raman","Finance","CA",99000,40,24000),
    ("Scott","Finance","NY",83000,36,19000),
    ("Jen","Finance","NY",79000,53,15000),
    ("Jeff","Marketing","CA",80000,25,18000),
    ("Kumar","Marketing","NY",91000,50,21000)
  ]

# Create DataFrame
schema = ["employee_name","department","state","salary","age","bonus"]
df = spark.createDataFrame(data=simpleData, schema = schema)
df.printSchema()
df.show(truncate=False)

Yields below output.

# Output:
+-------------+----------+-----+------+---+-----+
|employee_name|department|state|salary|age|bonus|
+-------------+----------+-----+------+---+-----+
|        James|     Sales|   NY| 90000| 34|10000|
|      Michael|     Sales|   NY| 86000| 56|20000|
|       Robert|     Sales|   CA| 81000| 30|23000|
|        Maria|   Finance|   CA| 90000| 24|23000|
|        Raman|   Finance|   CA| 99000| 40|24000|
|        Scott|   Finance|   NY| 83000| 36|19000|
|          Jen|   Finance|   NY| 79000| 53|15000|
|         Jeff| Marketing|   CA| 80000| 25|18000|
|        Kumar| Marketing|   NY| 91000| 50|21000|
+-------------+----------+-----+------+---+-----+

2. PySpark groupBy on DataFrame Columns

Let’s do the groupBy() on department column of DataFrame and then find the sum of salary for each department using sum() function.

Here’s how the groupBy() function works:

1. Grouping: You specify one or more columns in the groupBy() function to define the grouping criteria. Rows with identical values in the specified columns are grouped together into distinct groups.
2. Aggregation: After grouping the rows, you can apply aggregate functions such as COUNT, SUM, AVG, MIN, MAX, etc., to each group. These aggregate functions compute summary statistics for the rows within each group.

The groupBy() is commonly used in conjunction with aggregate functions to perform data summarization, generate reports, and derive insights from datasets. It allows you to analyze data at different levels of granularity by grouping rows based on specific attributes and computing aggregate statistics for each group.

# Using groupBy().sum()
df.groupBy("department").sum("salary").show(truncate=False)

# Output:
#+----------+-----------+
#|department|sum(salary)|
#+----------+-----------+
#|Sales     |257000     |
#|Finance   |351000     |
#|Marketing |171000     |
#+----------+-----------+

Similarly, we can calculate the number of employees in each department using.

# Using groupBy().count()
df.groupBy("department").count()

Calculate the minimum salary of each department using min()

# Using groupBy().min()
df.groupBy("department").min("salary")

Calculate the maximin salary of each department using max()

# Using groupBy().max()
df.groupBy("department").max("salary")

Calculate the average salary of each department using avg()

# Using groupBy().avg()
df.groupBy("department").avg( "salary")

Calculate the mean salary of each department using mean()

# Using groupBy().mean()
df.groupBy("department").mean( "salary") 

3. Using Multiple columns

Similarly, we can also run groupBy and aggregate on two or more DataFrame columns, below example does group by on department,state and does sum() on salary and bonus columns.

# GroupBy on multiple columns
df.groupBy("department","state") \
    .sum("salary","bonus") \
    .show(false)

This yields the below output.

# Output:
+----------+-----+-----------+----------+
|department|state|sum(salary)|sum(bonus)|
+----------+-----+-----------+----------+
|Finance   |NY   |162000     |34000     |
|Marketing |NY   |91000      |21000     |
|Sales     |CA   |81000      |23000     |
|Marketing |CA   |80000      |18000     |
|Finance   |CA   |189000     |47000     |
|Sales     |NY   |176000     |30000     |
+----------+-----+-----------+----------+

Similarly, we can run group by and aggregate on two or more columns for other aggregate functions; please refer to the example below.

4. Running more aggregates at a time

Alternatively, you can use groupBy().agg() to perform aggregation on DataFrame columns after grouping them based on one or more keys. It allows you to compute aggregate functions on grouped data, generating summary statistics for each group.

After grouping, you call the agg() method, which takes one or more pairs of column names and aggregation functions. The aggregation functions can include built-in functions like count(), sum(), avg(), min(), max(), etc., as well as user-defined functions.

from pyspark.sql.functions import sum,avg,max

# Running more aggregations
df.groupBy("department") \
    .agg(sum("salary").alias("sum_salary"), \
         avg("salary").alias("avg_salary"), \
         sum("bonus").alias("sum_bonus"), \
         max("bonus").alias("max_bonus") \
     ) \
    .show(truncate=False)

This code will produce a DataFrame with the aggregated statistics for each department, including the sum of salaries, average salary, sum of bonuses, and maximum bonus. The show() method displays the DataFrame content in tabular format, with the columns “department”, “sum_salary”, “avg_salary”, “sum_bonus”, and “max_bonus”.

# Output:
+----------+----------+-----------------+---------+---------+
|department|sum_salary|avg_salary       |sum_bonus|max_bonus|
+----------+----------+-----------------+---------+---------+
|Sales     |257000    |85666.66666666667|53000    |23000    |
|Finance   |351000    |87750.0          |81000    |24000    |
|Marketing |171000    |85500.0          |39000    |21000    |
+----------+----------+-----------------+---------+---------+

5. Using filter on aggregate data

from pyspark.sql.functions import sum,avg,max

# Using filter on aggregate data
df.groupBy("department") \
    .agg(sum("salary").alias("sum_salary"), \
      avg("salary").alias("avg_salary"), \
      sum("bonus").alias("sum_bonus"), \
      max("bonus").alias("max_bonus")) \
    .where(col("sum_bonus") >= 50000) \
    .show(truncate=False)

This removes the sum of a bonus that has less than 50000 and yields below output.

# Output:
+----------+----------+-----------------+---------+---------+
|department|sum_salary|avg_salary       |sum_bonus|max_bonus|
+----------+----------+-----------------+---------+---------+
|Sales     |257000    |85666.66666666667|53000    |23000    |
|Finance   |351000    |87750.0          |81000    |24000    |
+----------+----------+-----------------+---------+---------+

6. PySpark SQL GROUP BY Query

To run SQL queries in PySpark, you have to register the DataFrame as a temporary table/view. The createOrReplaceTempView() is a method available on DataFrame objects that allows you to register a DataFrame as a temporary view in the SparkSession. This temporary view acts as a pointer to the DataFrame and enables you to run SQL queries against it using Spark SQL.

After registering the DataFrame as a temporary view, you can write SQL queries against it using Spark SQL. These SQL queries can include various operations such as selection, filtering, grouping, joining, and aggregation, allowing you to perform data analysis and manipulation

The HAVING clause is used in conjunction with the GROUP BY clause to filter groups based on aggregate conditions. While the WHERE clause filters individual rows before grouping, the HAVING clause filters groups after grouping and aggregation have been performed.

# Register DataFrame as a temporary view
df.createOrReplaceTempView("employees")

# Using SQL Query
sql_string = """SELECT department,
       SUM(salary) AS sum_salary,
       AVG(salary) AS avg_salary,
       SUM(bonus) AS sum_bonus,
       MAX(bonus) AS max_bonus
FROM employees
GROUP BY department
HAVING SUM(bonus) >= 50000"""

# Execute SQL query against the temporary view
df2 = spark.sql(sql_string)
df2.show()

6. PySpark groupBy Example Source code

import pyspark
from pyspark.sql import SparkSession
from pyspark.sql.functions import col,sum,avg,max

spark = SparkSession.builder.appName('SparkByExamples.com').getOrCreate()

simpleData = [("James","Sales","NY",90000,34,10000),
    ("Michael","Sales","NY",86000,56,20000),
    ("Robert","Sales","CA",81000,30,23000),
    ("Maria","Finance","CA",90000,24,23000),
    ("Raman","Finance","CA",99000,40,24000),
    ("Scott","Finance","NY",83000,36,19000),
    ("Jen","Finance","NY",79000,53,15000),
    ("Jeff","Marketing","CA",80000,25,18000),
    ("Kumar","Marketing","NY",91000,50,21000)
  ]

schema = ["employee_name","department","state","salary","age","bonus"]
df = spark.createDataFrame(data=simpleData, schema = schema)
df.printSchema()
df.show(truncate=False)

df.groupBy("department").sum("salary").show(truncate=False)

df.groupBy("department").count().show(truncate=False)


df.groupBy("department","state") \
    .sum("salary","bonus") \
   .show(truncate=False)

df.groupBy("department") \
    .agg(sum("salary").alias("sum_salary"), \
         avg("salary").alias("avg_salary"), \
         sum("bonus").alias("sum_bonus"), \
         max("bonus").alias("max_bonus") \
     ) \
    .show(truncate=False)
    
df.groupBy("department") \
    .agg(sum("salary").alias("sum_salary"), \
      avg("salary").alias("avg_salary"), \
      sum("bonus").alias("sum_bonus"), \
      max("bonus").alias("max_bonus")) \
    .where(col("sum_bonus") >= 50000) \
    .show(truncate=False)

This example is also available at GitHub PySpark Examples project for reference.

7. Conclusion

In this tutorial, you have learned how to use groupBy() functions on PySpark DataFrame and also learned how to run these on multiple columns and finally filter data on the aggregated columns.

Thanks for reading. If you like it, please do share the article by following the below social links and any comments or suggestions are welcome in the comments sections! 

Happy Learning !!

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