Spark select top values in RDD

问题

The original dataset is:

# (numbersofrating,title,avg_rating)
newRDD =[(3,'monster',4),(4,'minions 3D',5),....] 

I want to select top N avg_ratings in newRDD.I use the following code,it has an error.

selectnewRDD = (newRDD.map(x, key =lambda x: x[2]).sortBy(......))

TypeError: map() takes no keyword arguments

The expected data should be:

# (numbersofrating,title,avg_rating)
selectnewRDD =[(4,'minions 3D',5),(3,'monster',4)....] 

回答1:

You can use either top or takeOrdered with key argument:

newRDD.top(2, key=lambda x: x[2])

or

newRDD.takeOrdered(2, key=lambda x: -x[2])

Note that top is taking elements in descending order and takeOrdered in ascending so key function is different in both cases.

回答2:

Have you tried using top? Given that you want the top avg ratings (and it is the third item in the tuple), you'll need to assign it to the key using a lambda function.

# items = (number_of_ratings, title, avg_rating)
newRDD = sc.parallelize([(3, 'monster', 4), (4, 'minions 3D', 5)])
top_n = 10
>>> newRDD.top(top_n, key=lambda items: items[2])
[(4, 'minions 3D', 5), (3, 'monster', 4)]

来源：https://stackoverflow.com/questions/31882221/spark-select-top-values-in-rdd