在浏览 Udacity 类(class)“Data Wrangling with MongoDB”时，他们有以下问题。我尝试解决(如下所示)。但是，它给了我 Python 错误，我不确定出了什么问题。
它发生的JSON格式是这样的:
{
"_id" : ObjectId("5304e2e3cc9e684aa98bef97"),
"text" : "First week of school is over :P",
"in_reply_to_status_id" : null,
"retweet_count" : null,
"contributors" : null,
"created_at" : "Thu Sep 02 18:11:25 +0000 2010",
"geo" : null,
"source" : "web",
"coordinates" : null,
"in_reply_to_screen_name" : null,
"truncated" : false,
"entities" : {
"user_mentions" : [ ],
"urls" : [ ],
"hashtags" : [ ]
},
"retweeted" : false,
"place" : null,
"user" : {
"friends_count" : 145,
"profile_sidebar_fill_color" : "E5507E",
"location" : "Ireland :)",
"verified" : false,
"follow_request_sent" : null,
"favourites_count" : 1,
"profile_sidebar_border_color" : "CC3366",
"profile_image_url" : "http://a1.twimg.com/profile_images/1107778717/phpkHoxzmAM_normal.jpg",
"geo_enabled" : false,
"created_at" : "Sun May 03 19:51:04 +0000 2009",
"description" : "",
"time_zone" : null,
"url" : null,
"screen_name" : "Catherinemull",
"notifications" : null,
"profile_background_color" : "FF6699",
"listed_count" : 77,
"lang" : "en",
"profile_background_image_url" : "http://a3.twimg.com/profile_background_images/138228501/149174881-8cd806890274b828ed56598091c84e71_4c6fd4d8-full.jpg",
"statuses_count" : 2475,
"following" : null,
"profile_text_color" : "362720",
"protected" : false,
"show_all_inline_media" : false,
"profile_background_tile" : true,
"name" : "Catherine Mullane",
"contributors_enabled" : false,
"profile_link_color" : "B40B43",
"followers_count" : 169,
"id" : 37486277,
"profile_use_background_image" : true,
"utc_offset" : null
},
"favorited" : false,
"in_reply_to_user_id" : null,
"id" : NumberLong("22819398300")
}
这里是带有说明的代码:
#!/usr/bin/env python
"""
Write an aggregation query to answer this question:
Of the users in the "Brasilia" timezone who have tweeted 100 times or more,
who has the largest number of followers?
The following hints will help you solve this problem:
- Time zone is found in the "time_zone" field of the user object in each tweet.
- The number of tweets for each user is found in the "statuses_count" field.
To access these fields you will need to use dot notation (from Lesson 4)
- Your aggregation query should return something like the following:
{u'ok': 1.0,
u'result': [{u'_id': ObjectId('52fd2490bac3fa1975477702'),
u'followers': 2597,
u'screen_name': u'marbles',
u'tweets': 12334}]}
Note that you will need to create the fields 'followers', 'screen_name' and 'tweets'.
Please modify only the 'make_pipeline' function so that it creates and returns an aggregation
pipeline that can be passed to the MongoDB aggregate function. As in our examples in this lesson,
the aggregation pipeline should be a list of one or more dictionary objects.
Please review the lesson examples if you are unsure of the syntax.
Your code will be run against a MongoDB instance that we have provided. If you want to run this code
locally on your machine, you have to install MongoDB, download and insert the dataset.
For instructions related to MongoDB setup and datasets please see Course Materials.
Please note that the dataset you are using here is a smaller version of the twitter dataset used
in examples in this lesson. If you attempt some of the same queries that we looked at in the lesson
examples, your results will be different.
"""
def get_db(db_name):
from pymongo import MongoClient
client = MongoClient('localhost:27017')
db = client[db_name]
return db
def make_pipeline():
# complete the aggregation pipeline
pipeline = [
{
"$match": {
"user.time_zone": "Brasilia",
"user.statuses_count": {"$gte": 100}
}
},
{
"$sort": { "$user.friends_count", -1}
},
{
"$limit": 1
},
{
"$project": {
"followers": "$user.friends_count",
"screen_name": "$user.screen_name",
"tweets": "$user.statuses_count"
}
}
]
return pipeline
def aggregate(db, pipeline):
result = db.tweets.aggregate(pipeline)
return result
if __name__ == '__main__':
db = get_db('twitter')
pipeline = make_pipeline()
result = aggregate(db, pipeline)
import pprint
pprint.pprint(result)
assert len(result["result"]) == 1
assert result["result"][0]["followers"] == 17209
这是它给我的错误:
Traceback (most recent call last):
File "vm_main.py", line 33, in <module>
import main
File "/tmp/vmuser_hnypkpkult/main.py", line 2, in <module>
import studentMain
File "/tmp/vmuser_hnypkpkult/studentMain.py", line 43, in <module>
result = aggregate(db, pipeline)
File "/tmp/vmuser_hnypkpkult/studentMain.py", line 37, in aggregate
result = db.tweets.aggregate(pipeline)
File "/usr/local/lib/python2.7/dist-packages/pymongo/collection.py", line 1390, in aggregate
"aggregate", self.__name, **command_kwargs)
File "/usr/local/lib/python2.7/dist-packages/pymongo/database.py", line 338, in _command
for doc in cursor:
File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1076, in next
if len(self.__data) or self._refresh():
File "/usr/local/lib/python2.7/dist-packages/pymongo/cursor.py", line 1020, in _refresh
self.__uuid_subtype))
bson.errors.InvalidDocument: Cannot encode object: set(['$user.friends_count', -1])
最佳答案
您的 $sort 子句被解释为 Python 集而不是字典。此外，我相信您需要引用该条款中没有美元符号的字段。将其更改为以下内容(注意冒号而不是逗号):
{
"$sort": { "user.friends_count": -1}
},
关于python - MongoDB 中的错误排序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/32639590/