"joinLeft" returns dataframe that smaller than left_df

[GBJim]

Hi all:

I found that leftJoin generates df that smaller than the left df

[In] [1]:  joined_flint = left_flint.leftJoin(right_flint, tolerance=tolerance, key=by)  
[In] [2]:  print (joined_flint.count() < left_flint.count())
True

I consider this is a false result since left join does not drop any row in the left table.
Any explanation or suggestion?

[placeybordeaux]

leftJoin doesn't have the same semantics as sql left join.

I thought this was really confusing as well.

futureLeftJoin A function performs the temporal future left-join to the right TimeSeriesRDD, i.e. left-join using inexact timestamp matches. For each row in the left, appends the closest future row from the right at or after the same time.

This means that if there were no rows with the matching key within the tolerance it will won't return any rows for that instance.