Testing Data Structures

Last updated on 2025-10-28 | Edit this page

Overview

Questions

How do you compare data structures such as lists and dictionaries?
How do you compare objects in libraries like pandas and numpy?

Objectives

Learn how to compare lists and dictionaries in Python.
Learn how to compare objects in libraries like pandas and numpy.

Data structures

When writing tests for your code, you often need to compare data structures such as lists, dictionaries, and objects from libraries like numpy and pandas. Here we will go over some of the more common data structures that you may use in research and how to test them.

Lists

Python lists can be tested using the usual == operator as we do for numbers.

PYTHON


def test_lists_equal():
    """Test that lists are equal"""
    # Create two lists
    list1 = [1, 2, 3]
    list2 = [1, 2, 3]
    # Check that the lists are equal
    assert list1 == list2

    # Two lists, different order
    list3 = [1, 2, 3]
    list4 = [3, 2, 1]
    assert list3 != list4

    # Create two different lists
    list5 = [1, 2, 3]
    list6 = [1, 2, 4]
    # Check that the lists are not equal
    assert list5 != list6

Note that the order of elements in the list matters. If you want to check that two lists contain the same elements but in different order, you can use the sorted function.

PYTHON

def test_sorted_lists_equal():
    """Test that lists are equal"""
    # Create two lists
    list1 = [1, 2, 3]
    list2 = [1, 2, 3]
    # Check that the lists are equal
    assert sorted(list1) == sorted(list2)

    # Two lists, different order
    list3 = [1, 2, 3]
    list4 = [3, 2, 1]
    assert sorted(list3) == sorted(list4)

    # Create two different lists
    list5 = [1, 2, 3]
    list6 = [1, 2, 4]
    # Check that the lists are not equal
    assert sorted(list5) != sorted(list6)

Dictionaries

Python dictionaries can also be tested using the == operator, however, the order of the keys does not matter. This means that if you have two dictionaries with the same keys and values, but in different order, they will still be considered equal.

The reason for this is that dictionaries are unordered collections of key-value pairs. (If you need to preserve the order of keys, you can use the collections.OrderedDict class.)

PYTHON

def test_dictionaries_equal():
    """Test that dictionaries are equal"""
    # Create two dictionaries
    dict1 = {"a": 1, "b": 2, "c": 3}
    dict2 = {"a": 1, "b": 2, "c": 3}
    # Check that the dictionaries are equal
    assert dict1 == dict2

    # Create two dictionaries, different order
    dict3 = {"a": 1, "b": 2, "c": 3}
    dict4 = {"c": 3, "b": 2, "a": 1}
    assert dict3 == dict4

    # Create two different dictionaries
    dict5 = {"a": 1, "b": 2, "c": 3}
    dict6 = {"a": 1, "b": 2, "c": 4}
    # Check that the dictionaries are not equal
    assert dict5 != dict6

numpy

Numpy is a common library used in research. Instead of the usual assert a == b, numpy has its own testing functions that are more suitable for comparing numpy arrays. These two functions are the ones you are most likely to use: - numpy.testing.assert_array_equal is used to compare two numpy arrays. - numpy.testing.assert_allclose is used to compare two numpy arrays with a tolerance for floating point numbers. - numpy.testing.assert_equal is used to compare two objects such as lists or dictionaries that contain numpy arrays.

Here are some examples of how to use these functions:

PYTHON


def test_numpy_arrays():
    """Test that numpy arrays are equal"""
    # Create two numpy arrays
    array1 = np.array([1, 2, 3])
    array2 = np.array([1, 2, 3])
    # Check that the arrays are equal
    np.testing.assert_array_equal(array1, array2)

# Note that np.testing.assert_array_equal even works with nested numpy arrays!

def test_nested_numpy_arrays():
    """Test that nested numpy arrays are equal"""
    # Create two nested numpy arrays
    array1 = np.array([[1, 2], [3, 4]])
    array2 = np.array([[1, 2], [3, 4]])
    # Check that the nested arrays are equal
    np.testing.assert_array_equal(array1, array2)

def test_numpy_arrays_with_tolerance():
    """Test that numpy arrays are equal with tolerance"""
    # Create two numpy arrays
    array1 = np.array([1.0, 2.0, 3.0])
    array2 = np.array([1.00009, 2.0005, 3.0001])
    # Check that the arrays are equal with tolerance
    np.testing.assert_allclose(array1, array2, atol=1e-3)

Callout

Data structures with numpy arrays

When you have data structures that contain numpy arrays, such as lists or dictionaries, you cannot use == to compare them. Instead, you can use numpy.testing.assert_equal to compare the data structures.

PYTHON

def test_dictionaries_with_numpy_arrays():
    """Test that dictionaries with numpy arrays are equal"""
    # Create two dictionaries with numpy arrays
    dict1 = {"a": np.array([1, 2, 3]), "b": np.array([4, 5, 6])}
    dict2 = {"a": np.array([1, 2, 3]), "b": np.array([4, 5, 6])}
    # Check that the dictionaries are equal
    np.testing.assert_equal(dict1, dict2)

pandas

Pandas is another common library used in research for storing and manipulating datasets. Pandas has its own testing functions that are more suitable for comparing pandas objects. These two functions are the ones you are most likely to use: - pandas.testing.assert_frame_equal is used to compare two pandas DataFrames. - pandas.testing.assert_series_equal is used to compare two pandas Series.

Here are some examples of how to use these functions:

PYTHON


def test_pandas_dataframes():
    """Test that pandas DataFrames are equal"""
    # Create two pandas DataFrames
    df1 = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
    df2 = pd.DataFrame({"A": [1, 2, 3], "B": [4, 5, 6]})
    # Check that the DataFrames are equal
    pd.testing.assert_frame_equal(df1, df2)

def test_pandas_series():
    """Test that pandas Series are equal"""
    # Create two pandas Series
    s1 = pd.Series([1, 2, 3])
    s2 = pd.Series([1, 2, 3])
    # Check that the Series are equal
    pd.testing.assert_series_equal(s1, s2)

Challenge

Checking if lists are equal

In statistics/stats.py add this function to remove anomalies from a list:

PYTHON

def remove_anomalies(data: list, maximum_value: float, minimum_value: float) -> list:
    """Remove anomalies from a list of numbers"""

    result = []

    for i in data:
        if i <= maximum_value and i >= minimum_value:
            result.append(i)
    
    return result

Then write a test for this function by comparing lists.

Show me the solution

PYTHON

from stats import remove_anomalies

def test_remove_anomalies():
    """Test remove_anomalies function"""
    data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
    maximum_value = 5
    minimum_value = 2
    expected_result = [2, 3, 4, 5]
    assert remove_anomalies(data, maximum_value, minimum_value) == expected_result

Challenge

Checking if dictionaries are equal

In statistics/stats.py add this function to calculate the frequency of each element in a list:

PYTHON

def calculate_frequency(data: list) -> dict:
    """Calculate the frequency of each element in a list"""

    frequencies = {}

    # Iterate over each value in the list
    for value in data:
        # If the value is already in the dictionary, increment the count
        if value in frequencies:
            frequencies[value] += 1
        # Otherwise, add the value to the dictionary with a count of 1
        else:
            frequencies[value] = 1

    return frequencies

Then write a test for this function by comparing dictionaries.

Show me the solution

PYTHON

from stats import calculate_frequency

def test_calculate_frequency():
    """Test calculate_frequency function"""
    data = [1, 2, 3, 1, 2, 1, 1, 3, 3, 3]
    expected_result = {1: 4, 2: 2, 3: 4}
    assert calculate_frequency(data) == expected_result

Challenge

Checking if numpy arrays are equal

In statistics/stats.py add this function to calculate the cumulative sum of a numpy array:

PYTHON

import numpy as np

def calculate_cumulative_sum(array: np.ndarray) -> np.ndarray:
    """Calculate the cumulative sum of a numpy array"""
    
    # don't use the built-in numpy function
    result = np.zeros(array.shape)
    result[0] = array[0]
    for i in range(1, len(array)):
        result[i] = result[i-1] + array[i]

    return result

Then write a test for this function by comparing numpy arrays.

Show me the solution

PYTHON

import numpy as np
from stats import calculate_cumulative_sum

def test_calculate_cumulative_sum():
    """Test calculate_cumulative_sum function"""
    array = np.array([1, 2, 3, 4, 5])
    expected_result = np.array([1, 3, 6, 10, 15])
    np.testing.assert_array_equal(calculate_cumulative_sum(array), expected_result)

Challenge

Checking if data structures with numpy arrays are equal

In statistics/stats.py add this function to calculate the total score of each player in a dictionary:

PYTHON


def calculate_player_total_scores(participants: dict):
    """Calculate the total score of each player in a dictionary.
    
    Example input:
    {
        "Alice": {
            "scores": np.array([1, 2, 3])
        },
        "Bob": {
            "scores": np.array([4, 5, 6])
        },
        "Charlie": {
            "scores": np.array([7, 8, 9])
        },
    }

    Example output:
    {
        "Alice": {
            "scores": np.array([1, 2, 3]),
            "total_score": 6
        },
        "Bob": {
            "scores": np.array([4, 5, 6]),
            "total_score": 15
        },
        "Charlie": {
            "scores": np.array([7, 8, 9]),
            "total_score": 24
        },
    }
    """"
    
    for player in participants:
        participants[player]["total_score"] = np.sum(participants[player]["scores"])

    return participants

Then write a test for this function by comparing dictionaries with numpy arrays.

Show me the solution

PYTHON

import numpy as np
from stats import calculate_player_total_scores

def test_calculate_player_total_scores():
    """Test calculate_player_total_scores function"""
    participants = {
        "Alice": {
            "scores": np.array([1, 2, 3])
        },
        "Bob": {
            "scores": np.array([4, 5, 6])
        },
        "Charlie": {
            "scores": np.array([7, 8, 9])
        },
    }
    expected_result = {
        "Alice": {
            "scores": np.array([1, 2, 3]),
            "total_score": 6
        },
        "Bob": {
            "scores": np.array([4, 5, 6]),
            "total_score": 15
        },
        "Charlie": {
            "scores": np.array([7, 8, 9]),
            "total_score": 24
        },
    }
    np.testing.assert_equal(calculate_player_total_scores(participants), expected_result)

Challenge

Checking if pandas DataFrames are equal

In statistics/stats.py add this function to calculate the average score of each player in a pandas DataFrame:

PYTHON

import pandas as pd

def calculate_player_average_scores(df: pd.DataFrame) -> pd.DataFrame:
    """Calculate the average score of each player in a pandas DataFrame.
    
    Example input:
    |   | player  | score_1 | score_2 |
    |---|---------|---------|---------|
    | 0 | Alice   | 1       | 2       |
    | 1 | Bob     | 3       | 4       |

    Example output:
    |   | player  | score_1 | score_2 | average_score |
    |---|---------|---------|---------|---------------|
    | 0 | Alice   | 1       | 2       | 1.5           |
    | 1 | Bob     | 3       | 4       | 3.5           |
    """

    df["average_score"] = df[["score_1", "score_2"]].mean(axis=1)

    return df

Then write a test for this function by comparing pandas DataFrames.

Hint: You can create a dataframe like this:

PYTHON

df = pd.DataFrame({
    "player": ["Alice", "Bob"],
    "score_1": [1, 3],
    "score_2": [2, 4]
})

Show me the solution

PYTHON

import pandas as pd
from stats import calculate_player_average_scores

def test_calculate_player_average_scores():
    """Test calculate_player_average_scores function"""
    df = pd.DataFrame({
        "player": ["Alice", "Bob"],
        "score_1": [1, 3],
        "score_2": [2, 4]
    })
    expected_result = pd.DataFrame({
        "player": ["Alice", "Bob"],
        "score_1": [1, 3],
        "score_2": [2, 4],
        "average_score": [1.5, 3.5]
    })
    pd.testing.assert_frame_equal(calculate_player_average_scores(df), expected_result)

Key Points

You can test equality of lists and dictionaries using the == operator.
Numpy arrays cannot be compared using the == operator. Instead, use numpy.testing.assert_array_equal and numpy.testing.assert_allclose.
Data structures that contain numpy arrays should be compared using numpy.testing.assert_equal.
Pandas DataFrames and Series should be compared using pandas.testing.assert_frame_equal and pandas.testing.assert_series_equal.