在 PySpark 数据框中添加一个可为空的列 [英] Adding a nullable column in PySpark dataframe

问题描述

在 Spark 中，文字列在添加时不可为空:

In Spark, literal columns, when added, are not nullable:

from pyspark.sql import SparkSession, functions as F
spark = SparkSession.builder.getOrCreate()

df = spark.createDataFrame([(1,)], ['c1'])

df = df.withColumn('c2', F.lit('a'))

df.printSchema()
#  root
#   |-- c1: long (nullable = true)
#   |-- c2: string (nullable = false)

如何创建可为空的列?

推荐答案

我发现的最短方法 - 使用 when(otherwise 子句似乎不需要):

The shortest method I've found - using when (the otherwise clause seems not needed):

df = df.withColumn('c2', F.when(F.lit(1).isNotNull(), F.lit('a')))

完整测试结果:

from pyspark.sql import SparkSession, functions as F
spark = SparkSession.builder.getOrCreate()

df = spark.createDataFrame([(1,)], ['c1'])
df = df.withColumn('c2', F.when(F.lit(1).isNotNull(), F.lit('a')))

df.show()
#  +---+---+
#  | c1| c2|
#  +---+---+
#  |  1|  a|
#  +---+---+

df.printSchema()
#  root
#   |-- c1: long (nullable = true)
#   |-- c2: string (nullable = true)

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