问题
I have a dataframe with as many as 10 million records. How can I get a count quickly? df.count is taking a very long time.
回答1:
It's going to take so much time anyway. At least the first time.
One way is to cache the dataframe, so you will be able to more with it, other than count.
E.g
df.cache()
df.count()
Subsequent operations don't take much time.
回答2:
file.groupBy("<column-name>").count().show()
来源：https://stackoverflow.com/questions/39357238/getting-the-count-of-records-in-a-data-frame-quickly