如何将嵌套的Struct列展开为多列？

Question

我正在尝试将具有嵌套struct类型(见下文)的DataFrame列扩展为多个列.我正在使用的Struct模式看起来像{"foo": 3, "bar": {"baz": 2}}.

理想情况下,我想将上面的内容扩展为两列("foo"和"bar.baz").然而,当我尝试使用.select("data.*")(其中data是结构柱),我只得到列foo和bar,其中bar仍然是一个struct.

有没有办法可以扩展两个图层的Struct？

Answer 1

我最终选择了以下递归“解开”分层结构的函数：

本质上，它不断挖掘Struct字段并保持其他字段完好无损，这种方法消除了df.select(...)在Struct有很多字段时需要很长的语句。这是代码：

# Takes in a StructType schema object and return a column selector that flattens the Struct
def flatten_struct(schema, prefix=""):
    result = []
    for elem in schema:
        if isinstance(elem.dataType, StructType):
            result += flatten_struct(elem.dataType, prefix + elem.name + ".")
        else:
            result.append(col(prefix + elem.name).alias(prefix + elem.name))
    return result


df = sc.parallelize([Row(r=Row(a=1, b=Row(foo="b", bar="12")))]).toDF()
df.show()
+----------+
|         r|
+----------+
|[1,[12,b]]|
+----------+

df_expanded = df.select("r.*")
df_flattened = df_expanded.select(flatten_struct(df_expanded.schema))

df_flattened.show()
+---+-----+-----+
|  a|b.bar|b.foo|
+---+-----+-----+
|  1|   12|    b|
+---+-----+-----+

Answer 2

您可以选择data.bar.baz为bar.baz:

df.show()
+-------+
|   data|
+-------+
|[3,[2]]|
+-------+

df.printSchema()
root
 |-- data: struct (nullable = false)
 |    |-- foo: long (nullable = true)
 |    |-- bar: struct (nullable = false)
 |    |    |-- baz: long (nullable = true)

在pyspark:

import pyspark.sql.functions as F
df.select(F.col("data.foo").alias("foo"), F.col("data.bar.baz").alias("bar.baz")).show()
+---+-------+
|foo|bar.baz|
+---+-------+
|  3|      2|
+---+-------+