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fer-gx-multi-batch

Validate multiple batches of an asset of a data source using Great Expectations Python Library.

Project context

This project is intended as a way to get to know "Great Expectations" Python library. It will rely on data coming from the NCY taxi data ( https://www.nyc.gov/site/tlc/about/tlc-trip-record-data.page ).

What can be achived?

By running the notebooks in this order:

  • a_file_data_context.ipynb

  • b_connect_to_source_data.ipynb

  • c_create_expectation_suite.ipynb

  • d_validate_multiple_batches.ipynb

You will get the results of validating multiple batches of a dataset against a criterion. The pattern can be applied to build a testing suite against data assets in your pipeline, being them source data as well as transformed data.

Example:

Data source asset

Screenshot of NYC taxi data asset

What to expect from that asset

  • Expect column fare_amount values to be between 5.0 and 100.0 at least for 90% of the records in each batch.

What we get from running validations

Validation Results for every batch

Validation Results for every batch

Notice that every batch ID has a year_ and a month_ prefix before year value and month value respectively. year and month are the names we defined for the group names when we created the asset.

Batch 2021-01: More than 10% of fare_amount column values lie outside of the expected value range Expectation was intentionally made to generate unexpected values

More than 10% of fare_amount column values lie outside of the expected value range

Batch 2021-02: Less than 10% of fare_amount column values lie outside of the expected value range

Less than 10% of fare_amount column values lie outside of the expected value range

Batch 2021-03 also has less than 10% of fare_amount column values lying outside of the expected value range.

Notebooks and their content

I separated the scripts into four different files in order to assure things are getting saved to the context (Context and other terms are explained below). The scripts and their function are as follows:

a_file_data_context.ipynb

This notebook contains code for:

  1. Install all the requirements.

  2. The creation of a data context that is persistent across python sessions. "One of the primary responsibilities of the DataContext is managing CRUD operations for core GX objects" .(GX = Great Expectations).

b_connect_to_source_data.ipynb

This notebook contains code for:

  1. The creation of the nyc_taxi_datasource data source.

  2. The creation of one asset for the data source called nyc_taxi_asset. The asset is composed by multiple batches (Multiple files).

c_create_expectation_suite.ipynb

This notebook contains code for:

  1. The creation of an expectation suite. An Expectation Suite is the placeholder for all the things you expect a certain data asset to conform to. Those things you expect are called Expectations.

    In this case, the expectation suite has the following expectation:

    • expect_column_values_to_be_between

  2. Saving of the created expectation suite into the persistent context.

d_validate_multiple_batches.ipynb

This notebook contains code for:

  1. The creation of a batch request with multiple batches.

  2. The creation of a validation list based on the batch request. Multiple files are going to be validated against the same Expectation Suite.

  3. Run the validation.

  4. Build and open the Data Docs in a browser. Data Docs are automatically generated by Great Expectations and show the Validation Results in a User friendly HTML presentation.

Virtual environment

Python version: 3.11.4

Great expectations version: 0.17.12

The gxmbvenv virtual environment has been created to control the environment dependencies and added to .gitignore to prevent it from beeing copied to the repository. requirements.txt will contain the required modules and versions for this project.

To install dependencies for this project run:

pip install -r requirements.txt

What I learned

Great expectations library allows the validation of assets composed of multiple files (Partitioned asset). In our case those files have a naming convention that allows the use of a Regular Expression to match all the files belonging to an asset.