Return a sampled subset of this RDD.
can elements be sampled multiple times (replaced when sampled out)
expected size of the sample as a fraction of this RDD’s size
without replacement: probability that each element is chosen; fraction must be [0, 1]
with replacement: expected number of times each element is chosen; fraction must be >= 0
seed for the random number generator
This is not guaranteed to provide exactly the fraction specified of the total
count of the given DataFrame.
>>> rdd = sc.parallelize(range(100), 4)
>>> 6 <= rdd.sample(False, 0.1, 81).count() <= 14