合并具有不同字段的数组结构列：Spark SQL高效解决方案-Python教程-PHP中文网

合并具有不同字段的数组结构列：spark sql高效解决方案

本文档旨在提供一种高效的方法，用于合并Spark DataFrame中两个包含不同字段的数组结构列。通过使用`transform`和`filter`函数，我们可以避免使用UDF，从而显著提高性能。本文将详细介绍实现步骤，并提供示例代码和注意事项，帮助读者轻松解决此类数据处理问题。

在Spark中，处理复杂的数据结构，例如包含数组的StructType，是很常见的任务。本文将介绍如何有效地合并两个具有不同字段的数组结构列，并避免使用用户定义函数 (UDF)，从而提高性能。

问题描述

假设我们有一个DataFrame，其中包含两个数组结构的列：materials和elastic。 materials包含id和percentage字段，而elastic包含id和name字段。我们的目标是创建一个新的数组结构列merged_materials，它包含id、percentage和name字段，并且materials.id与elastic.id相匹配。

解决方案：使用transform和filter

Spark SQL提供了内置函数transform和filter，可以有效地处理数组。我们可以使用transform迭代第一个数组（materials），然后使用filter在第二个数组（elastic）中查找相应的条目。

以下是使用PySpark实现的示例代码：

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from pyspark.sql import functions as F
from pyspark.sql.types import StructType, StructField, IntegerType, FloatType, MapType, StringType, ArrayType

# 模拟测试数据
testdata = """
  {"product_id": 1, "tenant_id": 1, "materials": [{"id": 1, "percentage": 0.1}, {"id": 3, "percentage": 0.3}, {"id": 2, "percentage": 0.2}], "elastic": [{"id": 1, "name": {"en": "one", "fr": "un"}},{"id":2, "name": {"en": "two", "fr": "deux"}}] }
"""
# 定义Schema
schema = StructType([
    StructField('product_id', IntegerType(), True),
    StructField('tenant_id', IntegerType(), True),
    StructField("materials", ArrayType(StructType([
        StructField('id', IntegerType(), True),
        StructField('percentage', FloatType(), True)
    ]))),
    StructField("elastic", ArrayType(StructType([
        StructField('id', IntegerType(), True),
        StructField('name', MapType(StringType(), StringType()), True)
    ])))
])

df = spark.read.json(spark.sparkContext.parallelize([testdata]), schema=schema)


# 创建一个新的列，其中包含合并后的数组
df = df.withColumn(
    "merged_materials",
    F.expr("""
        transform(
            materials,
            m -> named_struct(
                'id', m.id,
                'percentage', m.percentage,
                'name', filter(elastic, e -> e.id == m.id)[0].name
            )
        )
    """)
)

df.show(vertical=True, truncate=False)

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代码解释:

transform(materials, m -> ...): 此函数迭代materials数组，并将每个元素作为m传递给lambda表达式。
named_struct('id', m.id, 'percentage', m.percentage, 'name', ...): 此函数创建一个新的结构体，包含id、percentage和name字段。
filter(elastic, e -> e.id == m.id)[0].name: 此函数过滤elastic数组，查找id与m.id匹配的元素，并提取其name字段。 [0] 用于获取过滤后的第一个元素，因为我们期望每个materials.id在elastic中最多只有一个匹配项。

输出:

-RECORD 0-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------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-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------0
 elastic          | [{1, Map(en -> one, fr -> un)}, {2, Map(en -> two, fr -> deux)}]
 materials        | [{1, 0.1}, {3, 0.3}, {2, 0.2}]                                    
 merged_materials | [{1, 0.1, Map(en -> one, fr -> un)}, {3, 0.3, null}, {2, 0.2, Map(en -> two, fr -> deux)}]
 product_id       | 1                                                                 
 tenant_id        | 1

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注意事项:

如果elastic中没有与materials.id匹配的条目，则name字段将为null。
此方法假设elastic中每个id都是唯一的。如果不是这种情况，filter函数将返回多个匹配项，并且[0]将仅选择第一个匹配项。
如果elastic为空，则filter函数将抛出异常，因为没有元素可以被索引。为了避免这种情况，您可以在filter之前添加一个检查，以确保elastic不为空。