为什么在
然而现在,至少有一列的
DataFrame
中不存在NaN值的情况下,有些函数执行后会使用nullable = true
?val myDf = Seq((2,"A"),(2,"B"),(1,"C"))
.toDF("foo","bar")
.withColumn("foo", 'foo.cast("Int"))
myDf.withColumn("foo_2", when($"foo" === 2 , 1).otherwise(0)).select("foo", "foo_2").show
当现在调用df.printSchema
时,nullable
对于两个列都将是false
。
val foo: (Int => String) = (t: Int) => {
fooMap.get(t) match {
case Some(tt) => tt
case None => "notFound"
}
}
val fooMap = Map(
1 -> "small",
2 -> "big"
)
val fooUDF = udf(foo)
myDf
.withColumn("foo", fooUDF(col("foo")))
.withColumn("foo_2", when($"foo" === 2 , 1).otherwise(0)).select("foo", "foo_2")
.select("foo", "foo_2")
.printSchema
然而现在,至少有一列的
nullable
属性从之前的false
变为了true
。这是如何解释的?