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Pandas and Spark DataFrame comparison for humans

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DataComPy is a package to compare two Pandas DataFrames. Originally started to be something of a replacement for SAS's

for Pandas DataFrames with some more functionality than just
(in that it prints out some stats, and lets you tweak how accurate matches have to be). Then extended to carry that functionality over to Spark Dataframes.

Quick Installation


pip install datacompy

Pandas Detail

DataComPy will try to join two dataframes either on a list of join columns, or on indexes. If the two dataframes have duplicates based on join values, the match process sorts by the remaining fields and joins based on that row number.

Column-wise comparisons attempt to match values even when dtypes don't match. So if, for example, you have a column with

values in one dataframe and an identically-named column with
dtype in another, it will tell you that the dtypes are different but will still try to compare the values.

Basic Usage

.. code-block:: python

from io import StringIO
import pandas as pd
import datacompy

data1 = """acct_id,dollar_amt,name,float_fld,date_fld 10000001234,123.45,George Maharis,14530.1555,2017-01-01 10000001235,0.45,Michael Bluth,1,2017-01-01 10000001236,1345,George Bluth,,2017-01-01 10000001237,123456,Bob Loblaw,345.12,2017-01-01 10000001239,1.05,Lucille Bluth,,2017-01-01 """

data2 = """acct_id,dollar_amt,name,float_fld 10000001234,123.4,George Michael Bluth,14530.155 10000001235,0.45,Michael Bluth, 10000001236,1345,George Bluth,1 10000001237,123456,Robert Loblaw,345.12 10000001238,1.05,Loose Seal Bluth,111 """

df1 = pd.read_csv(StringIO(data1)) df2 = pd.read_csv(StringIO(data2))

compare = datacompy.Compare( df1, df2, join_columns='acct_id', #You can also specify a list of columns abs_tol=0, #Optional, defaults to 0 rel_tol=0, #Optional, defaults to 0 df1_name='Original', #Optional, defaults to 'df1' df2_name='New' #Optional, defaults to 'df2' ) compare.matches(ignore_extra_columns=False)


This method prints out a human-readable report summarizing and sampling differences


See docs for more detailed usage instructions and an example of the report output.

Things that are happening behind the scenes

  • You pass in two dataframes (

    ) to
    and a column to join on (or list of columns) to
    . By default the comparison needs to match values exactly, but you can pass in
    to apply absolute and/or relative tolerances for numeric columns.
    • You can pass in
      instead of
      to join on the index instead.
  • The class validates that you passed dataframes, that they contain all of the columns in

    and have unique column names other than that. The class also lowercases all column names to disambiguate.
  • On initialization the class validates inputs, and runs the comparison.

  • Compare.matches()
    will return
    if the dataframes match,
    • You can pass in
      to not return
      just because there are non-overlapping column names (will still check on overlapping columns)
    • NOTE: if you only want to validate whether a dataframe matches exactly or not, you should look at
      . The main use case for
      is when you need to interpret the difference between two dataframes.
  • Compare also has some shortcuts like

    • intersect_rows
      for getting intersection, just df1 and just df2 records (DataFrames)
    • intersect_columns()
      for getting intersection, just df1 and just df2 columns (Sets)
  • You can turn on logging to see more detailed logs.

.. _spark-detail:

Spark Detail


class will join two dataframes either on a list of join columns. It has the capability to map column names that may be different in each dataframe, including in the join columns. You are responsible for creating the dataframes from any source which Spark can handle and specifying a unique join key. If there are duplicates in either dataframe by join key, the match process will remove the duplicates before joining (and tell you how many duplicates were found).

As with the Pandas-based

class, comparisons will be attempted even if dtypes don't match. Any schema differences will be reported in the output as well as in any mismatch reports, so that you can assess whether or not a type mismatch is a problem or not.

The main reasons why you would choose to use

are that your data is too large to fit into memory, or you're comparing data that works well in a Spark environment, like partitioned Parquet, CSV, or JSON files, or Cerebro tables.

Performance Implications

Spark scales incredibly well, so you can use

to compare billions of rows of data, provided you spin up a big enough cluster. Still, joining billions of rows of data is an inherently large task, so there are a couple of things you may want to take into consideration when getting into the cliched realm of "big data":
  • SparkCompare
    will compare all columns in common in the dataframes and report on the rest. If there are columns in the data that you don't care to compare, use a
    statement/method on the dataframe(s) to filter those out. Particularly when reading from wide Parquet files, this can make a huge difference when the columns you don't care about don't have to be read into memory and included in the joined dataframe.
  • For large datasets, adding
    to the
    call can help optimize performance by caching certain intermediate dataframes in memory, like the de-duped version of each input dataset, or the joined dataframe. Otherwise, Spark's lazy evaluation will recompute those each time it needs the data in a report or as you access instance attributes. This may be fine for smaller dataframes, but will be costly for larger ones. You do need to ensure that you have enough free cache memory before you do this, so this parameter is set to False by default.

Basic Usage

.. code-block:: python

import datetime
import datacompy
from pyspark.sql import Row

This example assumes you have a SparkSession named "spark" in your environment, as you

do when running pyspark from the terminal or in a Databricks notebook (Spark v2.0 and higher)

data1 = [ Row(acct_id=10000001234, dollar_amt=123.45, name='George Maharis', float_fld=14530.1555,, 1, 1)), Row(acct_id=10000001235, dollar_amt=0.45, name='Michael Bluth', float_fld=1.0,, 1, 1)), Row(acct_id=10000001236, dollar_amt=1345.0, name='George Bluth', float_fld=None,, 1, 1)), Row(acct_id=10000001237, dollar_amt=123456.0, name='Bob Loblaw', float_fld=345.12,, 1, 1)), Row(acct_id=10000001239, dollar_amt=1.05, name='Lucille Bluth', float_fld=None,, 1, 1)) ]

data2 = [ Row(acct_id=10000001234, dollar_amt=123.4, name='George Michael Bluth', float_fld=14530.155), Row(acct_id=10000001235, dollar_amt=0.45, name='Michael Bluth', float_fld=None), Row(acct_id=10000001236, dollar_amt=1345.0, name='George Bluth', float_fld=1.0), Row(acct_id=10000001237, dollar_amt=123456.0, name='Robert Loblaw', float_fld=345.12), Row(acct_id=10000001238, dollar_amt=1.05, name='Loose Seal Bluth', float_fld=111.0) ]

base_df = spark.createDataFrame(data1) compare_df = spark.createDataFrame(data2)

comparison = datacompy.SparkCompare(spark, base_df, compare_df, join_columns=['acct_id'])

This prints out a human-readable report summarizing differences

Using SparkCompare on EMR or standalone Spark

  1. Set proxy variables
  2. Create a virtual environment, if desired (
    virtualenv venv; source venv/bin/activate
  3. Pip install datacompy and requirements
  4. Ensure your SPARK_HOME environment variable is set (this is probably
    but may differ based on your installation)
  5. Augment your PYTHONPATH environment variable with
    (note that your version of py4j may differ depending on the version of Spark you're using)

Using SparkCompare on Databricks

  1. Clone this repository locally
  2. Create a datacompy egg by running
    python bdist_egg
    from the repo root directory.
  3. From the Databricks front page, click the "Library" link under the "New" section.
  4. On the New library page: a. Change source to "Upload Python Egg or PyPi" b. Under "Upload Egg", Library Name should be "datacompy" c. Drag the egg file in datacompy/dist/ to the "Drop library egg here to upload" box d. Click the "Create Library" button
  5. Once the library has been created, from the library page (which you can find in your /Users/{login} workspace), you can choose clusters to attach the library to.
  6. import datacompy
    in a notebook attached to the cluster that the library is attached to and enjoy!


We welcome and appreciate your contributions! Before we can accept any contributions, we ask that you please be sure to sign the

Contributor License Agreement (CLA) 

This project adheres to the

Open Source Code of Conduct 
_. By participating, you are expected to honor this code.


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