pyspark-iris

The pyspark-iris Kedro starter

Introduction

The code in this repository demonstrates best practice when working with Kedro and PySpark. It contains a Kedro starter template with some initial configuration and an example pipeline, and originates from the Kedro documentation about how to work with PySpark.

Getting started

The starter template can be used to start a new project using the starter option in kedro new:

kedro new --starter=pyspark-iris

As a reference, the How to use Kedro on a Databricks cluster tutorial bootstraps the project using this starter.

Features

Single configuration in /conf/base/spark.yml

While Spark allows you to specify many different configuration options, this starter uses /conf/base/spark.yml as a single configuration location.

SparkSession initialisation

This Kedro starter contains the initialisation code for SparkSession in the ProjectContext and takes its configuration from /conf/base/spark.yml. Modify this code if you want to further customise your SparkSession, e.g. to use YARN.

Configures MemoryDataSet to work with Spark objects

Out of the box, Kedro's MemoryDataSet works with Spark's DataFrame. However, it doesn't work with other Spark objects such as machine learning models unless you add further configuration. This Kedro starter demonstrates how to configure MemoryDataSet for Spark's machine learning model in the catalog.yml.

Note: The use of MemoryDataSet is encouraged to propagate Spark's DataFrame between nodes in the pipeline. A best practice is to delay triggering Spark actions for as long as needed to take advantage of Spark's lazy evaluation.

An example machine learning pipeline that uses only PySpark and Kedro

This Kedro starter uses the simple and familiar Iris dataset. It contains the code for an example machine learning pipeline that trains a random forest classifier to classify an iris.

The pipeline includes two modular pipelines: one for data engineering and one for data science.

The data engineering pipeline includes:

• A node to transform multiple features into a single-column features vector using VectorAssembler, as well as convert a textual representation of the label column into a numerical one using StringIndexer
• A node to split the transformed data into training dataset and testing dataset using a configurable ratio

The data science pipeline includes:

• A node to train the random forest classifier using pyspark.ml.classification.RandomForestClassifier
• A node to make predictions using this classifier on the testing dataset
• A node to evaluate the model based on its predictions using pyspark.ml.evaluation.MulticlassClassificationEvaluator