How to compare 2 dataframes in python unittest using assert methods

Question

I'm writing unittest for a method that returns a dataframe, but, while testing the output using:

self.asserEquals(mock_df, result)

I'm getting ValueError:

ValueError: The truth value of a DataFrame is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

Right now I'm comparing properties that serves the purpose now,

self.assertEqual(mock_df.size, result.size)
self.assertEqual(mock_df.col_a.to_list(), result.col_a.to_list())
self.assertEqual(mock_df.col_b.to_list(), result.col_b.to_list())
self.assertEqual(mock_df.col_c.to_list(), result.col_c.to_list())

but curious how do I assert dataframes.

BioData41 · Accepted Answer · 2022-06-29 00:56:07Z

8

The accepted answer from @Mahi did not work for me. It failed for two Dataframes that should have been equal. Not sure why.

As I discovered here under "DataFrame equality", there are some functions built into Pandas for testing.

The following worked for me. I tested it several times, but not exhaustively, to make sure it would work repeatedly.

import unittest
import pandas as pd

class test_something(unittest.TestCase):
    def test_method(self):
        #... create dataframes df1 and df2...
        pd.testing.assert_frame_equal(df1,df2)

Here is related pandas reference for the above function.

answered Jun 29, 2022 at 0:56

BioData41

1,03211 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Juha Palomäki Over a year ago

assert_frame_equal is good for testing. If the test fails, it also shows the differences between the two dataframes.

Mahi · Accepted Answer · 2021-10-12 05:19:43Z

6

import unittest
import pandas as pd

class TestDataFrame(unittest.TestCase):
    def test_dataframe(self):
        df1 = pd.DataFrame({'a': [1, 2], 'b': [3, 4]})
        df2 = pd.DataFrame({'a': [1, 2], 'b': [3.0, 4.0]})
        self.assertEqual(True, df1.equals(df2))

if __name__ == '__main__':
    unittest.main()

answered Oct 12, 2021 at 5:19

Mahi

3603 silver badges11 bronze badges

3 Comments

AkshayJain Over a year ago

Thanks, Mahi, though it's working in some cases. For a few I get AssertionError visually the data looks the same and is indexed properly.

BioData41 Over a year ago

I also had an issue with this approach not working. I found an alternate approach that worked and posted that as an alternate answer.

Yaoyu Yang Over a year ago

I think you can simplify slightly using self.assertTrue(df1.equals(df2))

mountrix · Accepted Answer · 2025-10-19 16:26:23Z

0

The answer of @BioData41 is working for me, however assert_frame_equal is throwing an exception if the comparison is failing.

For a simple boolean result, I am using this:

test_df1 = df1.reset_index(drop=True)[list(df2.columns)]
test_df2 = df2.reset_index(drop=True)
test_df1.compare(test_df2).empty # Should return True or False

answered Oct 19 at 16:26

mountrix

1,2522 gold badges17 silver badges36 bronze badges

Collectives™ on Stack Overflow

How to compare 2 dataframes in python unittest using assert methods

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related