17 March 2020

Python Compare Two Lists of Dictionaries

development

In this post, we look at how to compare two lists of dictionaries in Python and also print out the differences between the two lists.

The comparison method compares keys and values in the dictionaries.

Also, the ordering of elements does not matter when comparing two lists of dictionaries in Python.

Compare list of dictionaries in Python

if __name__ == '__main__':

    list_1 = [
        {'id': '123-abc', 'name': 'Mike', 'age': 40},
        {'name': 'John', 'age': 34, 'id': '123-efg'},
        {'age': 32, 'id': '123-xyz', 'name': 'Aly'}
    ]

    list_2 = [
        {'name': 'Mike', 'id': '123-abc', 'age': 40},
        {'id': '123-efg', 'age': 34, 'name': 'John'},
        {'id': '123-xyz', 'name': 'Aly', 'age': 32}
    ]

    assert [i for i in list_1 if i not in list_2] == []

In the above code, list_1 and list_2 are equal. That is, each dictionary contains the same items (keys and values) in both lists. The order of elements in each dictionary is irrelevant.

Compare list of dictionaries - print differences

We can also print which dictionary items are different in the lists:

For example:

if __name__ == '__main__':

    list_1 = [
        {'id': '123-abc', 'name': 'Mike', 'age': 40},
        {'id': '123-efg', 'name': 'John', 'age': 24},
        {'id': '123-xyz', 'name': 'Aly', 'age': 35}
    ]

    list_2 = [
        {'id': '123-abc', 'name': 'Mike', 'age': 40},
        {'id': '123-efg', 'name': 'Jon', 'age': 24},
        {'id': '123-xyz', 'name': 'Aly', 'age': 32}
    ]

    for i in list_1:
        if i not in list_2:
            print(i)

Output:

{'id': '123-efg', 'name': 'John', 'age': 24}
{'id': '123-xyz', 'name': 'Aly', 'age': 35}

Another way to write the above method is:

def compare_two_lists(list1: list, list2: list) -> bool:
    """
    Compare two lists and logs the difference.
    :param list1: first list.
    :param list2: second list.
    :return:      if there is difference between both lists.
    """
    diff = [i for i in list1 + list2 if i not in list1 or i not in list2]
    result = len(diff) == 0
    if not result:
        print(f'There are {len(diff)} differences:\n{diff[:5]}')
    return result

Convert Two Lists Using Pandas DataFrame

The example code below shows how to compare two lists using Pandas DataFrame

from pandas import DataFrame
import pandas as pd

def compare_two_lists(list1: list, list2: list) -> bool:
    """
    Compare two lists and logs the difference.
    :param list1: first list.
    :param list2: second list.
    :return:      if there is difference between both lists.
    """
    df1 = pd.DataFrame(list1)
    df2 = pd.DataFrame(list2)
    diff = dataframe_difference(df1, df2)
    result = len(diff) == 0
    if not result:
        print(f'There are {len(diff)} differences:\n{diff.head()}')
    return result

def dataframe_difference(df1: DataFrame, df2: DataFrame) -> DataFrame:
    """
    Find rows which are different between two DataFrames.
    :param df1: first dataframe.
    :param df2: second dataframe.
    :return:    if there is different between both dataframes.
    """
    comparison_df = df1.merge(df2, indicator=True, how='outer')
    diff_df = comparison_df[comparison_df['_merge'] != 'both']
    return diff_df

17 March 2020