How to Combine Two PySpark DataFrames Side by Side

What will you learn?

In this tutorial, you will learn how to horizontally concatenate or join two PySpark DataFrames side by side seamlessly without losing any information.

Introduction to the Problem and Solution

When working with PySpark, there may arise a need to merge two DataFrames side by side. This can be achieved through column-wise concatenation using the union function in PySpark. By adding a unique row index to each DataFrame and joining them based on these indices, you can combine the data horizontally while preserving all the original information from both DataFrames.


from pyspark.sql import SparkSession
from pyspark.sql.functions import monotonically_increasing_id

# Create Spark session
spark = SparkSession.builder.appName("merge_dataframes").getOrCreate()

# Create sample DataFrames df1 and df2
data1 = [(1, "Alice"), (2, "Bob"), (3, "Charlie")]
data2 = [(4, "David"), (5, "Eve"), (6, "Frank")]

columns = ["id", "name"]

df1 = spark.createDataFrame(data=data1, schema=columns)
df2 = spark.createDataFrame(data=data2, schema=columns)

# Add a unique row index to each DataFrame
df1 = df1.withColumn("row_index", monotonically_increasing_id())
df2 = df2.withColumn("row_index", monotonically_increasing_id())

# Join DataFrames on the row_index column
result_df = df1.join(df2, on=["row_index"], how="inner").drop("row_index")

# Copyright PHD


To achieve horizontal concatenation of two PySpark DataFrames: – Initiate a Spark session. – Generate sample data for demonstration. – Utilize monotonically_increasing_id function to assign unique row indices. – Merge the DataFrames based on these indices. – Remove the redundant row index column from the final result.

This method ensures a seamless combination of both datasets while maintaining their individual information within a single DataFrame.

    How do I install PySpark?

    To install PySpark via pip, use pip install pyspark.

    Can I concatenate more than two DataFrames using this method?

    Yes, you can extend this technique to merge multiple DataFrames by incorporating additional columns with unique identifiers and performing corresponding joins.

    Is it possible to customize join conditions when combining DataFrames?

    Absolutely! You can specify various join types like ‘left’, ‘right’, or ‘outer’ joins as per your requirements during DataFrame merging.

    Does this method preserve the original order of rows in each DataFrame?

    Yes, as we add unique identifiers before merging based on them; it retains the original row order from both initial datasets.

    Can I apply filters or transformations before combining these datasets?

    Certainly! You can execute necessary transformations or filters prior to horizontal concatenation as illustrated in our provided code snippet above.

    Will there be performance implications when merging large datasets using this approach?

    While performance may vary depending on dataset size and cluster setup; generally horizontal concatenation scales well even for larger datasets owing to Apache Spark’s distributed processing capabilities supporting PySpark functionality.


    In conclusion: Merging PySpark DataFrames horizontally involves creating unique identifiers for rows in each DataFrame followed by joining them based on these identifiers. By following this outlined procedure; users can seamlessly merge disparate datasets while retaining all pertinent information within the resulting composite dataset. This enables comprehensive analysis and insights derived through a consolidated view enriched by merged contents.

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