I have to calculate the number of times a user has tweeted, with data being in a JSON file. I tried `groupByKey` and `reduceByKey` but the output is user id and the tweet itself, not the count of tweets. 

Code: 

```
from pyspark import SparkContext
from pyspark.sql import SQLContext

sc = SparkContext("local", "Twitter")
sqlc = SQLContext(sc)

df = sqlc.read.json("file.json")
tweets = df.select("user.id","text")
users = tweets.rdd.reduceByKey(lambda x,y:x+y)

```

How do I get the count of tweets by their respective users as key?