根据特定键合并两个词典列表

Question

Ok, so I have this code.

data1 = [
    {'Id': 1}, 
    {'Id': 2}
]
data2 = [
    {'Id': 1, 'score': 100, 'testdata': 333}, 
    {'Id': 2, 'score': 200, 'testdata': 555}, 
    {'Id': 3, 'score': 300, 'testdata': 444}
]

expectedData = [
        {'Id': 1, 'Score': 100}, 
        {'Id': 2, 'Score': 200}
    ]


def merge_lists(data1, data2, key):
    merged = {}
    for item in data1+data2:
        if item[key] in merged:
            merged[item[key]].update(item)
        else:
            merged[item[key]] = item
    return [val for (_, val) in merged.items()]

merged = merge_lists(data1, data2, 'Id')

print merged

The problem is that this will merge every value(that's not 'id') in data2 into data1. I only want it to merge the key 'score', but I'm really not sure how to specify that key only. I've tried multiple other conditional statements in order to specify the 'score' key. But I can't seem to get anything working.

Thanks for any help

Answer 1

You could factory function like this

data1 = [
    {'Id': 1},
    {'Id': 2}
]
data2 = [
    {'Id': 1, 'score': 100, 'testdata': 333},
    {'Id': 2, 'score': 200, 'testdata': 555},
    {'Id': 3, 'score': 300, 'testdata': 444}
]

def get_score(list_of_dict, id_value):

    for dict_ in list_of_dict:
        if dict_["Id"] == id_value:
            return {"score": dict_["score"]}

res = data1.copy()

for dict_ in res:
    dict_.update(get_score(data2, dict_["Id"]))

print(res)
# [{'score': 100, 'Id': 1}, {'score': 200, 'Id': 2}]

Answer 2

Here's code that will merge the way you want. Note that if there are multiple lists in data2 with the correct matching key only the first one will be found.

data1 = [
    {'Id': 1}, 
    {'Id': 2},
]

data2 = [
    {'Id': 1, 'score': 100, 'testdata': 333}, 
    {'Id': 2, 'score': 200, 'testdata': 555}, 
    {'Id': 3, 'score': 300, 'testdata': 444},
]

def merge_lists(data1, data2, key):
    result = []
    for d1 in data1:
        val = d1[key]
        dnew = {key: val}
        for d2 in data2:
            if d2[key] == val:
                dnew['score'] = d2['score']
                break
        else:
            raise KeyError('No match for %r: %s' % (key, val))
        result.append(dnew)
    return result

merged = merge_lists(data1, data2, 'Id')
print merged

output

[{'score': 100, 'Id': 1}, {'score': 200, 'Id': 2}]

If we change data1 to

data1 = [
    {'Id': 1}, 
    {'Id': 5},
    {'Id': 2},
]

Then we get this output:

Traceback (most recent call last):
  File "./qtest.py", line 45, in <module>
    merged = merge_lists(data1, data2, 'Id')
  File "./qtest.py", line 41, in merge_lists
    raise KeyError('No match for %r: %s' % (key, val))
KeyError: "No match for 'Id': 5"