scala - 如何将dataframe中的空值填充到uuid？

Question

有一个数据框有一列为空值(并非全部为空)，需要用uuid填充空值，有办法吗？

cala> val df = Seq(("stuff2",null,null), ("stuff2",null,Array("value1","value2")),("stuff3","stuff3",null)).toDF("field","field2","values")
        df: org.apache.spark.sql.DataFrame = [field: string, field2: string, values: array<string>]

        scala> df.show
        +------+------+----------------+
        | field|field2|          values|
        +------+------+----------------+
        |stuff2|  null|            null|
        |stuff2|  null|[value1, value2]|
        |stuff3|stuff3|            null|
        +------+------+----------------+

我尝试了这种方式，但是“field2”的每一行都有相同的uuid。

scala> val fillDF = df.na.fill(java.util.UUID.randomUUID().toString(), Seq("field2"))
    fillDF: org.apache.spark.sql.DataFrame = [field: string, field2: string, values: array<string>]

scala> fillDF.show
+------+--------------------+----------------+
| field|              field2|          values|
+------+--------------------+----------------+
|stuff2|d007ffae-9134-4ac...|            null|
|stuff2|d007ffae-9134-4ac...|[value1, value2]|
|stuff3|              stuff3|            null|
+------+--------------------+----------------+

如何制作呢？如果超过 1,000,000 行

Answer 1

您可以使用 UDF 和 coalesce 来完成此操作，如下所示。

import org.apache.spark.sql.functions.udf
val arr = udf(() => java.util.UUID.randomUUID().toString())

val df2 = df.withColumn("field2", coalesce(df("field2"), arr()))
df2.show()

您将获得如下所示的不同 UUID。

+------+--------------------+----------------+
| field|              field2|          values|
+------+--------------------+----------------+
|stuff2|fda6bc42-1265-407...|            null|
|stuff2|3fa74767-abd7-405...|[value1, value2]|
|stuff3|              stuff3|            null|
+------+--------------------+----------------+