6
为什么在执行某些函数后nullable = true?在df中仍然没有nan值。火花为什么列更改为可空
val myDf = Seq((2,"A"),(2,"B"),(1,"C"))
.toDF("foo","bar")
.withColumn("foo", 'foo.cast("Int"))
myDf.withColumn("foo_2", when($"foo" === 2 , 1).otherwise(0)).select("foo", "foo_2").show
时df.printSchema
被称为现在可空将是两列假的。
val foo: (Int => String) = (t: Int) => {
fooMap.get(t) match {
case Some(tt) => tt
case None => "notFound"
}
}
val fooMap = Map(
1 -> "small",
2 -> "big"
)
val fooUDF = udf(foo)
myDf
.withColumn("foo", fooUDF(col("foo")))
.withColumn("foo_2", when($"foo" === 2 , 1).otherwise(0)).select("foo", "foo_2")
.select("foo", "foo_2")
.printSchema
但是现在,对于至少一个之前为假的列,可为空值为真。这怎么解释?