Python - Two (slightly different) JSON arrays Comparison

Question

i need to compare the two JSON arrays below, and end up with the below emails_new result ... The stick in the mud I'm finding is one of the arrays has an extra key/value pair, which I need in the updated array. So struggling to match.

Essentially; 'if any email(s) in emails_exist appear in emails_all, don't include them as part of emails_new'

Existing Arrays

emails_all = [{'email': '[email protected]', 'first_name': 'New Name'}, {'email': '[email protected]', 'first_name': 'Exists Name'}]

emails_exist = [{'email': '[email protected]'}]

Removing all of the emails_exist values from the emails_all, I only want to build a list to show the email/first_name of the emails that do not appear in emails_exist ... Similar to the below emails_new

Output

emails_new = [{'email': '[email protected]', 'first_name': 'New'}]

Possibly worthy of note: these JSON arrays may have up to 100 items in each.

as far as I can tell, your question has nothing to do with JSON — juanpa.arrivillaga
– juanpa.arrivillaga, Commented May 27, 2018 at 8:48

Peter · Accepted Answer · 2018-05-27 08:50:59Z

2

Just use a simple helper function

def contains(emails, email):                      
    for contained_email in emails:                   
        if email["email"] == contained_email["email"]: 
            return True                                 
    return False                                    

emails_new = [email for email in emails_all if not contains(emails_exist, email)]

answered May 27, 2018 at 8:50

Peter

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3 Comments

Danny Over a year ago

Very clever @peter , and for my lack of sleep brain, this 'simple helper' function is liquid Adderall, thanks. One thing, the resulting array still need to have the first_name key/value ... Currently it spits out the [{'email': '[email protected]'},] only. Possible?

Peter Over a year ago

@Danny Are you sure? The new array contains only entries from emails_all wihtout modifying them in any way. They should still contain the first_name. It just filters out the entries that return True using the contains function.

Danny Over a year ago

Ugh, apologies, I'm on no sleep ... I'd removed the ProjectionExpression from the DDB call while testing, what a 15 years in the business, amateur. Thanks Peter, this works perfectly. I do not

hygull · Accepted Answer · 2018-05-27 11:45:19Z

@Danny, you can also get the expected output with just 1 line of code using Python's list comprehension, map(), filter(), lambda function etc. as the below code examples shows.

Please comment if you face any problem while reading & understanding my code.

Check Lambda, filter(), map() and List comprehension. It's really good to use these concepts in programming.

1 line code

emails_new = list(filter(lambda email_all_dict: True if sum(list(map(lambda email_exist_dict: True if email_exist_dict["email"] == email_all_dict['email'] else False, emails_exist))) == 0 else False, emails_all))

Now have a look at the below code examples one by one.

Example 1

emails_all = [{'email': '[email protected]', 'first_name': 'New Name'}, {'email': '[email protected]', 'first_name': 'Exists Name'}]

emails_exist = [{'email': '[email protected]'}]

emails_new = list(filter(lambda email_all_dict: True if sum(list(map(lambda email_exist_dict: True if email_exist_dict["email"] == email_all_dict['email'] else False, emails_exist))) == 0 else False, emails_all))

print(emails_new)

# [{'first_name': 'New Name', 'email': '[email protected]'}]

Example 2

emails_all = [
        {'email': '[email protected]', 'first_name': 'New Name1'}, 
        {'email': '[email protected]', 'first_name': 'Exists Name1'},
        {'email': '[email protected]', 'first_name': 'Exists Name2'},
        {'email': '[email protected]', 'first_name': 'Exists Name5'},
        {'email': '[email protected]', 'first_name': 'Exists Name6'},
        {'email': '[email protected]', 'first_name': 'New Name9'}, 
        {'email': '[email protected]', 'first_name': 'Exists Name7'},
        {'email': '[email protected]', 'first_name': 'Exists Name8'},
        {'email': '[email protected]', 'first_name': 'Exists Name4'},
        {'email': '[email protected]', 'first_name': 'New Name4'}, 
        {'email': '[email protected]', 'first_name': 'New Name2'}, 
        {'email': '[email protected]', 'first_name': 'Exists Name3'}
]

emails_exist = [
        {'email': '[email protected]'},    # Does not exist
        {'email': '[email protected]', 'first_name': 'Exists Name7'},
        {'email': '[email protected]', 'first_name': 'Exists Name8'},
        {'email': '[email protected]', 'first_name': 'Exists Name4'}
]

emails_new2 = list(filter(lambda email_all_dict: True if sum(list(map(lambda email_exist_dict: True if email_exist_dict["email"] == email_all_dict['email'] else False, emails_exist))) == 0 else False, emails_all))

# Pretty printing list
print(json.dumps(emails_new2, indent=4))

"""
[
    {
        "first_name": "New Name1",
        "email": "[email protected]"
    },
    {
        "first_name": "Exists Name1",
        "email": "[email protected]"
    },
    {
        "first_name": "Exists Name2",
        "email": "[email protected]"
    },
    {
        "first_name": "Exists Name5",
        "email": "[email protected]"
    },
    {
        "first_name": "Exists Name6",
        "email": "[email protected]"
    },
    {
        "first_name": "New Name9",
        "email": "[email protected]"
    },
    {
        "first_name": "New Name4",
        "email": "[email protected]"
    },
    {
        "first_name": "New Name2",
        "email": "[email protected]"
    },
    {
        "first_name": "Exists Name3",
        "email": "[email protected]"
    }
]
"""

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