While working with a huge dataset Python pandas DataFrame is not good enough to perform complex transformation operations on big data set, hence if you have a Spark cluster, it’s better to convert pandas to PySpark DataFrame, apply the complex transformations on Spark cluster, and convert it back.
In this article, I will explain the steps in converting pandas to PySpark DataFrame and how to Optimize the pandas to PySpark DataFrame Conversion by enabling Apache Arrow.
1. Create pandas DataFrame
To convert pandas to PySpark DataFrame first, let’s create Pandas DataFrame with some test data. To use pandas you have to import it first using import pandas as pd
import pandas as pd
data = [['Scott', 50], ['Jeff', 45], ['Thomas', 54],['Ann',34]]
# Create the pandas DataFrame
pandasDF = pd.DataFrame(data, columns = ['Name', 'Age'])
# print dataframe.
print(pandasDF)
# Prints below Pandas DataFrame
Name Age
0 Scott 50
1 Jeff 45
2 Thomas 54
3 Ann 34
Operations on Pyspark run faster than Python pandas due to its distributed nature and parallel execution on multiple cores and machines. In other words, pandas run operations on a single node whereas PySpark runs on multiple machines. If you are working on a Machine Learning application where you are dealing with larger datasets it’s a good option to consider PySpark. PySpark processes operations many times faster than pandas.
2. Convert Pandas to PySpark (Spark) DataFrame
Spark provides a createDataFrame(pandas_dataframe) method to convert pandas to Spark DataFrame, Spark by default infers the schema based on the pandas data types to PySpark data types.
from pyspark.sql import SparkSession
#Create PySpark SparkSession
spark = SparkSession.builder \
.master("local[1]") \
.appName("SparkByExamples.com") \
.getOrCreate()
#Create PySpark DataFrame from Pandas
sparkDF=spark.createDataFrame(pandasDF)
sparkDF.printSchema()
sparkDF.show()
#Outputs below schema & DataFrame
root
|-- Name: string (nullable = true)
|-- Age: long (nullable = true)
+------+---+
| Name|Age|
+------+---+
| Scott| 50|
| Jeff| 45|
|Thomas| 54|
| Ann| 34|
+------+---+
If you want all data types to String use spark.createDataFrame(pandasDF.astype(str)).
3. Change Column Names & DataTypes while Converting
If you want to change the schema (column name & data type) while converting pandas to PySpark DataFrame, create a PySpark Schema using StructType and use it for the schema.
from pyspark.sql.types import StructType,StructField, StringType, IntegerType
#Create User defined Custom Schema using StructType
mySchema = StructType([ StructField("First Name", StringType(), True)\
,StructField("Age", IntegerType(), True)])
#Create DataFrame by changing schema
sparkDF2 = spark.createDataFrame(pandasDF,schema=mySchema)
sparkDF2.printSchema()
sparkDF2.show()
#Outputs below schema & DataFrame
root
|-- First Name: string (nullable = true)
|-- Age: integer (nullable = true)
+----------+---+
|First Name|Age|
+----------+---+
| Scott| 50|
| Jeff| 45|
| Thomas| 54|
| Ann| 34|
+----------+---+
4. Use Apache Arrow to Convert pandas to Spark DataFrame
Apache Spark uses Apache Arrow which is an in-memory columnar format to transfer the data between Python and JVM. You need to enable to use of Arrow as this is disabled by default and have Apache Arrow (PyArrow) install on all Spark cluster nodes using pip install pyspark[sql] or by directly downloading from Apache Arrow for Python.
spark.conf.set("spark.sql.execution.arrow.enabled","true")
sparkDF=spark.createDataFrame(pandasDF)
sparkDF.printSchema()
sparkDF.show()
You need to have Spark compatible Apache Arrow installed to use the above statement, In case you have not installed Apache Arrow you get the below error.
\apps\Anaconda3\lib\site-packages\pyspark\sql\pandas\conversion.py:289: UserWarning: createDataFrame attempted Arrow optimization because 'spark.sql.execution.arrow.pyspark.enabled' is set to true; however, failed by the reason below:
PyArrow >= 0.15.1 must be installed; however, it was not found.
Attempting non-optimization as 'spark.sql.execution.arrow.pyspark.fallback.enabled' is set to true.
When an error occurs, Spark automatically fallback to non-Arrow optimization implementation, this can be controlled by spark.sql.execution.arrow.pyspark.fallback.enabled.
spark.conf.set("spark.sql.execution.arrow.pyspark.fallback.enabled","true")
Note: Apache Arrow currently support all Spark SQL data types except MapType, ArrayType of TimestampType, and nested <a href="https://sparkbyexamples.com/pyspark/pyspark-structtype-and-structfield/">StructType</a>.
5. Complete Example of Convert pandas to Spark Dataframe
Belo is a complete example to convert pandas to PySpark DataFrame.
import pandas as pd
data = [['Scott', 50], ['Jeff', 45], ['Thomas', 54],['Ann',34]]
# Create the pandas DataFrame
pandasDF = pd.DataFrame(data, columns = ['Name', 'Age'])
# print dataframe.
print(pandasDF)
from pyspark.sql import SparkSession
spark = SparkSession.builder \
.master("local[1]") \
.appName("SparkByExamples.com") \
.getOrCreate()
sparkDF=spark.createDataFrame(pandasDF)
sparkDF.printSchema()
sparkDF.show()
#sparkDF=spark.createDataFrame(pandasDF.astype(str))
from pyspark.sql.types import StructType,StructField, StringType, IntegerType
mySchema = StructType([ StructField("First Name", StringType(), True)\
,StructField("Age", IntegerType(), True)])
sparkDF2 = spark.createDataFrame(pandasDF,schema=mySchema)
sparkDF2.printSchema()
sparkDF2.show()
# Enable Apache Arrow to convert Pandas to PySpark DataFrame
spark.conf.set("spark.sql.execution.arrow.enabled","true")
sparkDF2=spark.createDataFrame(pandasDF)
sparkDF2.printSchema()
sparkDF2.show()
#Convert PySpark DataFrame to Pandas
pandasDF2=sparkDF2.select("*").toPandas
print(pandasDF2)
Conclusion
In this article, you have learned how easy to convert pandas to Spark DataFrame and optimize the conversion using Apache Arrow (in-memory columnar format)
Happy Learning!!
Thank you ma’am/sir. This is exactly what I needed.