Iterating a list of dictionaries and creating a result set by comparing two lists

Question

We have two lists in the below format:

list_A = [
    {u'salary': 11, u'id': 1, u'name': u'adam'},
    {u'salary': 22, u'id': 2, u'name': u'ben'},
    {u'salary': 33, u'id': 3, u'name': u'charles'}
]

list_B = [
    {u'salary': 101, u'id': 1, u'name': u'adam'},
    {u'salary': 44, u'id': 4, u'name': u'david'}
]

How do I get id if common in both, then select from list B?

res = [
    {u'salary': 101, u'id': 1, u'name': u'adam'},
    {u'salary': 22, u'id': 2, u'name': u'ben'},
    {u'salary': 33, u'id': 3, u'name': u'charles'},
    {u'salary': 44, u'id': 4, u'name': u'david'}
]

I tried a for loop iterating on list A checking element in B and appending to empty list res, but was not able to achieve the desired result.

id is unique element. list A is old , list B is new, so we have to append the list B to list A overwriting the other elements , in this case, salary is updated for Adam.

Are your `id` values *unique* in either list? Then just convert your lists to dictionaries. — Martijn Pieters, Jan 20 '20 at 17:01
no, the goal here is - list A is old , list B is new, so we have to append the list B to list A overwriting the common elements , in this case, salary is updated for Adam, — Vidya K, Jan 20 '20 at 17:02
Does this answer your question? [How do I merge two dictionaries in a single expression?](https://stackoverflow.com/questions/38987/how-do-i-merge-two-dictionaries-in-a-single-expression) — blkpingu, Jan 20 '20 at 17:11

score 1 · Accepted Answer · answered Jan 20 '20 at 17:08

You can put your data in a dictionary and use the update method to make the necessary changes.

list_A = [
    {u'salary': 11, u'id': 1, u'name': u'adam'},
    {u'salary': 22, u'id': 2, u'name': u'ben'},
    {u'salary': 33, u'id': 3, u'name': u'charles'}
]

list_B = [
    {u'salary': 101, u'id': 1, u'name': u'adam'},
    {u'salary': 44, u'id': 4, u'name': u'david'}
]

data = {d['id']: d for d in list_A}
new_data = {d['id']: d for d in list_B}

data.update(new_data)

res = list(data.values())

score 1 · Answer 2 · answered Jan 20 '20 at 17:09

1

Use dictionaries:

by_id = {d['id']: d for d in list_A}
by_id.update({d['id']: d for d in list_B})

You can avoid creating the second dictionary by using a lazy generator:

by_id.update((d['id'], d) for d in list_B)

answered Jan 20 '20 at 17:09

Mad Physicist

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Iterating a list of dictionaries and creating a result set by comparing two lists

2 Answers2