python - pyspark:计算列表中不同元素的出现次数

Question

我必须以下数据:

data = {'date': ['2014-01-01', '2014-01-02', '2014-01-03', '2014-01-04', '2014-01-05', '2014-01-06'],
     'flat': ['A;A;B', 'D;P;E;P;P', 'H;X', 'P;Q;G', 'S;T;U', 'G;C;G']}

data['date'] = pd.to_datetime(data['date'])

data = pd.DataFrame(data)
data['date'] = pd.to_datetime(data['date'])
spark = SparkSession.builder \
    .master('local[*]') \
    .config("spark.driver.memory", "500g") \
    .appName('my-pandasToSparkDF-app') \
    .getOrCreate()
spark.conf.set("spark.sql.execution.arrow.enabled", "true")
spark.sparkContext.setLogLevel("OFF")

df=spark.createDataFrame(data)
new_frame = df.withColumn("list", F.split("flat", "\;"))

我想添加一个新列，用于保存每个不同元素的出现次数(按升序排序)，以及另一列用于保存最大值:

+-------------------+-----------+---------------------+-----------+----+
|               date| flat      | list                |occurrences|max |
+-------------------+-----------+---------------------+-----------+----+
|2014-01-01 00:00:00|A;A;B      |['A','A','B']        |[1,2]      |2   |
|2014-01-02 00:00:00|D;P;E;P;P  |['D','P','E','P','P']|[1,1,3]    |3   |
|2014-01-03 00:00:00|H;X        |['H','X']            |[1,1]      |1   |
|2014-01-04 00:00:00|P;Q;G      |['P','Q','G']        |[1,1,1]    |1   |
|2014-01-05 00:00:00|S;T;U      |['S','T','U']        |[1,1,1]    |1   |
|2014-01-06 00:00:00|G;C;G      |['G','C','G']        |[1,2]      |2   |  
+-------------------+-----------+---------------------+-----------+----+

非常感谢!

Answer 1

对于Spark2.4+，这可以无需多个groupBy和聚合来实现(因为它们是大型中昂贵的洗牌操作数据)。您可以使用高阶函数的一个表达式来实现此目的 变换和>聚合。这应该是spark2.4的规范解决方案。

from pyspark.sql import functions as F
df=spark.createDataFrame(data)
df.withColumn("list", F.split("flat","\;"))\
  .withColumn("occurances", F.expr("""array_sort(transform(array_distinct(list), x-> aggregate(list, 0,(acc,t)->acc+IF(t=x,1,0))))"""))\
  .withColumn("max", F.array_max("occurances"))\
  .show()
+-------------------+---------+---------------+----------+---+
|               date|     flat|           list|occurances|max|
+-------------------+---------+---------------+----------+---+
|2014-01-01 00:00:00|    A;A;B|      [A, A, B]|    [1, 2]|  2|
|2014-01-02 00:00:00|D;P;E;P;P|[D, P, E, P, P]| [1, 1, 3]|  3|
|2014-01-03 00:00:00|      H;X|         [H, X]|    [1, 1]|  1|
|2014-01-04 00:00:00|    P;Q;G|      [P, Q, G]| [1, 1, 1]|  1|
|2014-01-05 00:00:00|    S;T;U|      [S, T, U]| [1, 1, 1]|  1|
|2014-01-06 00:00:00|    G;C;G|      [G, C, G]|    [1, 2]|  2|
+-------------------+---------+---------------+----------+---+