在python中合并两个字典列表以创建第三个

Question

假设我有以下几点：

list_a = [
    {u'username': u'firstuser', u'userid': u'1'},
    {u'username': u'seconduser', u'userid': u'2'},
    {u'username': u'thirduser', u'userid': u'3'},
]

还有这个：

list_b = [
    {u'username': u'firstuser', u'userid': u'101'},
    {u'username': u'seconduser', u'userid': u'102'},
]

我怎样才能得到这样的第三个：

list_result = [
    {u'username': u'firstuser', u'userid_one': u'1', u'userid_two': u'101'},
    {u'username': u'seconduser', u'userid_one': u'2', u'userid_two': u'102'},
    {u'username': u'thirduser', u'userid_one': u'3', u'userid_two': u''},
]

Answer 1

您可以通过以下方式在几行代码中实现所需的结果：

list_a = [
    {u'username': u'firstuser', u'userid': u'1'},
    {u'username': u'seconduser', u'userid': u'2'},
    {u'username': u'thirduser', u'userid': u'3'},
]

list_b = [
    {u'username': u'firstuser', u'userid': u'101'},
    {u'username': u'seconduser', u'userid': u'102'},
]

# Get all users from both lists.
users = set(elem['username'] for elem in list_a + list_b)
# Get all ids for every user from the above list we created.
userids = [{user:[elem['userid'] for elem in list_a + list_b if elem['username']==user]} for user in users]
# Add a padding of a maximum of two elements in order to fill any missing values with ''.
userids = [{key: ids + [''] * (2-len(ids))} for user in userids for key , ids in user.items()]
# Create final list.
list_c = [{'username':key, 'userid_one':values[0], 'userid_two':values[1]} for elem in userids for key, values in elem.items()]
print(list_c)

最终结果：

[{'username': 'seconduser', 'userid_one': '2', 'userid_two': '102'}, {'username': 'thirduser', 'userid_one': '3', 'userid_two': ''}, {'username': 'firstuser', 'userid_one': '1', 'userid_two': '101'}]

Answer 2

最后我做了以下几点（在看到两个新答案之前）：

final_list = []

for i in range(0, len(list_a)):
    d = {}
    userid_two = ''
    d['username'] = list_a[i]['username']
    for j in range(0, len(list_b)):
        if d['username'] == list_b[j]['username']:
            userid_two = list_b[j]['userid']
    d['userid_two'] = userid_two
    d['userid_one'] = list_a[i]['userid']
    final_list.append(d)

它看起来很接近最近的答案，但我不知道什么是最好的方式做这件事

Answer 3

您可以为两个输入列表中的每一个构建dict，如下所示：

dict_a = {
    e['username']: e['userid']
    for e in list_a}
dict_b = {
    e['username']: e['userid']
    for e in list_b}

---

然后构建一个新的dict组合来自以下两个方面的数据：

dict_result = {}

for username, userid in dict_a.items():
    if username not in dict_result:
        dict_result[username] = {}
    dict_result[username]['userid_one'] = userid
for username, userid in dict_b.items():
    if username not in dict_result:
        dict_result[username] = {}
    dict_result[username]['userid_two'] = userid

这也可以缩短为：

import collections
dict_result = collections.defaultdict(dict)

for label, d in [('one', dict_a), ('two', dict_b)]
    for username, userid in d.items():
        dict_result[username]['userid_{}'.format(label)] = userid

---

最后，如果您真的需要最终结果作为列表：

list_result = []

for username, d in dict_result.items():
    # 'd' already contains the other data, we just add the 'username'
    d['username'] = username

    list_result.append(d)