如何根据PySpark中的数组值进行过滤？

Question

我的架构:

|-- Canonical_URL: string (nullable = true)
 |-- Certifications: array (nullable = true)
 |    |-- element: struct (containsNull = true)
 |    |    |-- Certification_Authority: string (nullable = true)
 |    |    |-- End: string (nullable = true)
 |    |    |-- License: string (nullable = true)
 |    |    |-- Start: string (nullable = true)
 |    |    |-- Title: string (nullable = true)
 |-- CompanyId: string (nullable = true)
 |-- Country: string (nullable = true)
|-- vendorTags: array (nullable = true)
 |    |-- element: struct (containsNull = true)
 |    |    |-- score: double (nullable = true)
 |    |    |-- vendor: string (nullable = true)

我尝试了以下查询来从中选择嵌套字段 vendorTags

df3 = sqlContext.sql("select vendorTags.vendor from globalcontacts")

如何where在PySpark中查询下面的子句中的嵌套字段

df3 = sqlContext.sql("select vendorTags.vendor from globalcontacts where vendorTags.vendor = 'alpha'")

要么

df3 = sqlContext.sql("select vendorTags.vendor from globalcontacts where vendorTags.score > 123.123456")

像这样的东西..

我尝试上述查询只是为了得到以下错误

df3 = sqlContext.sql("select vendorTags.vendor from globalcontacts where vendorTags.vendor = 'alpha'")

16/03/15 13:16:02 INFO ParseDriver: Parsing command: select vendorTags.vendor from globalcontacts where vendorTags.vendor = 'alpha'
16/03/15 13:16:03 INFO ParseDriver: Parse Completed
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/spark/python/pyspark/sql/context.py", line 583, in sql
    return DataFrame(self._ssql_ctx.sql(sqlQuery), self)
  File "/usr/lib/spark/python/lib/py4j-0.9-src.zip/py4j/java_gateway.py", line 813, in __call__
  File "/usr/lib/spark/python/pyspark/sql/utils.py", line 51, in deco
    raise AnalysisException(s.split(': ', 1)[1], stackTrace)
pyspark.sql.utils.AnalysisException: u"cannot resolve '(vendorTags.vendor = cast(alpha as double))' due to data type mismatch: differing types in '(vendorTags.vendor = cast(alpha as double))' (array<string> and double).; line 1 pos 71"

Answer 1

对于基于相等的查询,您可以使用array_contains:

df = sc.parallelize([(1, [1, 2, 3]), (2, [4, 5, 6])]).toDF(["k", "v"])
df.registerTempTable("df")

# With SQL
sqlContext.sql("SELECT * FROM df WHERE array_contains(v, 1)")

# With DSL
from pyspark.sql.functions import array_contains
df.where(array_contains("v", 1))

如果要使用更复杂的谓词,则必须使用explode或使用UDF,例如:

from pyspark.sql.types import BooleanType
from pyspark.sql.functions import udf 

def exists(f):
    return udf(lambda xs: any(f(x) for x in xs), BooleanType())

df.where(exists(lambda x: x > 3)("v"))

在Spark 2.4中.或者以后也可以使用更高阶的函数

df.where(expr("""aggregate(
    transform(v, x -> x > 3),
    false, 
    (x, y) -> x or y
)"""))

Answer 2

在 spark 2.4 中，您可以使用 sql API 中的 filter 函数过滤数组值。

https://spark.apache.org/docs/2.4.0/api/sql/index.html#filter

这是pyspark中的示例。在示例中，我们过滤掉所有空字符串的数组值：

df = df.withColumn("ArrayColumn", expr("filter(ArrayColumn, x -> x != '')"))