def evaluate(truth: RDD, prediction: RDD) -> float:
"""
Calculate RMSE between truth and predictions.
:param truth: RDD<Hashable, Hashable, float> = RDD<(bucket, item, rating)>
:param prediction: RDD<Hashable, Hashable, float> = RDD<(bucket, item, rating)>
:return: float = RMSE
"""
truth = truth.map(lambda u: ((u[0], u[1]), u[2]))
prediction = prediction.map(lambda u: ((u[0], u[1]), u[2]))
return truth.join(prediction).map(lambda u:
(u[1][0] - u[1][1])**2).mean()**0.5
def _join(rdd: RDD, other: RDD, func=None):
num_partitions = max(rdd.getNumPartitions(), other.getNumPartitions())
rtn_rdd = rdd.join(other, numPartitions=num_partitions)
if func is not None:
rtn_rdd = _map_value(rtn_rdd, lambda x: func(x[0], x[1]))
return rtn_rdd
