Github user mengxr commented on a diff in the pull request:
https://github.com/apache/spark/pull/7755#discussion_r35923142
--- Diff: python/pyspark/sql/dataframe.py ---
@@ -441,6 +441,42 @@ def sample(self, withReplacement, fraction, seed=None):
rdd = self._jdf.sample(withReplacement, fraction, long(seed))
return DataFrame(rdd, self.sql_ctx)
+ @since(1.5)
+ def sampleBy(self, col, fractions, seed=None):
+ """
+ Returns a stratified sample without replacement based on the
+ fraction given on each stratum.
+
+ :param col: column that defines strata
+ :param fractions:
+ sampling fraction for each stratum. If a stratum is not
+ specified, we treat its fraction as zero.
+ :param seed: random seed
+ :return: a new DataFrame that represents the stratified sample
+
+ >>> from pyspark.sql.functions import col
+ >>> dataset = sqlContext.range(0, 100).select((col("id") %
3).alias("key"))
+ >>> sampled = dataset.sampleBy("key", fractions={0: 0.1, 1: 0.2},
seed=0)
+ >>> sampled.groupBy("key").count().orderBy("key").show()
+ +---+-----+
+ |key|count|
+ +---+-----+
+ | 0| 3|
--- End diff --
This is different from Scala output because we use different number of
threads in python unit tests. See
https://issues.apache.org/jira/browse/SPARK-9487.
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