如何在pyspark中将字符串聚合到字典中的结果？答案

【问题标题】：How to aggregate string to dictionary like results in pyspark?如何在pyspark中将字符串聚合到字典中的结果？
【发布时间】：2018-06-25 09:26:20
【问题描述】：

我有一个数据框，我想每天汇总。

data = [
    (125, '2012-10-10','good'),
    (20, '2012-10-10','good'),
    (40, '2012-10-10','bad'),
    (60, '2012-10-10','NA')]
df = spark.createDataFrame(data, ["temperature", "date","performance"])

我可以使用 spark 内置函数（如 max、min、avg）来聚合数值。如何聚合字符串？

我希望是这样的：

date	max_temp	min_temp	performance_frequency
2012-10-10	125	20	"good": 2, "bad":1, "NA":1

【问题讨论】：

标签： string aggregation

【解决方案1】：

我们可以使用 MapType 和 UDF 和 Counter 来返回值计数，

from pyspark.sql import functions as F
from pyspark.sql.types import MapType,StringType,IntegerType
from collections import Counter

data = [(125, '2012-10-10','good'),(20, '2012-10-10','good'),(40, '2012-10-10','bad'),(60, '2012-10-10','NA')]
df = spark.createDataFrame(data, ["temperature", "date","performance"])

udf1 = F.udf(lambda x: dict(Counter(x)),MapType(StringType(),IntegerType()))

df.groupby('date').agg(F.min('temperature'),F.max('temperature'),udf1(F.collect_list('performance')).alias('performance_frequency')).show(1,False)
+----------+----------------+----------------+---------------------------------+
|date      |min(temperature)|max(temperature)|performance_frequency            |
+----------+----------------+----------------+---------------------------------+
|2012-10-10|20              |125             |Map(NA -> 1, bad -> 1, good -> 2)|
+----------+----------------+----------------+---------------------------------+

df.groupby('date').agg(F.min('temperature'),F.max('temperature'),udf1(F.collect_list('performance')).alias('performance_frequency')).collect()
[Row(date='2012-10-10', min(temperature)=20, max(temperature)=125, performance_frequency={'bad': 1, 'good': 2, 'NA': 1})]

希望这会有所帮助！

【讨论】：