Aggregate query with avg on pymongo get nan

Question

I have an issue with the Average function in pymongo aggregate query.

I have a structure like this:

{'_id': ObjectId('5afd9c675e3a1f0e9b830510'),
  'actor_gender': 'NaN',
  'actor_id': 'NaN',
  'actor_last_name': 'Safary',
  'actor_name': 'Darsheel',
  'actor_role': 'NaN',
  'director_id': 'NaN',
  'director_last_name': 'Khan',
  'director_name': 'Aamir',
  'movie_genre': 'Drama',
  'movie_name': 'Taare Zameen Par',
  'movie_rank': 8.5,
  'movie_year': 2007}

When I compute this query:

coll.aggregate([{"$group":{"_id":{"movie_genre":"Drama"},
                    "avg":{"$avg":"$movie_rank"}}}])

I got this nan on the average:

{'_id': {'movie_genre': 'Drama'}, 'avg': nan}

Answer 1

具有nan值的Mongodb聚合将NAN作为输出（ https://jira.mongodb.org/plugins/servlet/mobile#issue/SERVER-27472 ）您必须在movie_rank字段中具有一些nan值。