scala - 如何根据条件(组中的值)更新列？

Question

我有以下 df:

+---+----+-----+
|sno|dept|color|
+---+----+-----+
|  1|  fn|  red|
|  2|  fn| blue|
|  3|  fn|green|
+---+----+-----+

如果任何颜色列值是 red ，那么我颜色列的所有值都应该更新为 red ， 如下:

+---+----+-----+
|sno|dept|color|
+---+----+-----+
|  1|  fn|  red|
|  2|  fn|  red|
|  3|  fn|  red|
+---+----+-----+

我想不通。请帮忙;我试过以下代码:

val gp=jdbcDF.filter($"dept".contains("fn"))
     //.withColumn("newone",when($"dept"==="fn","RED").otherwise("NULL"))
    gp.show()
gp.map(
  row=>{
    val row1=row.getAs[String](1)
    var row2=row.getAs[String](2)
    val make=if(row1 =="fn") row2="red"
    Row(row(0),row(1),make)
  }
).collect().foreach(println)

Answer 1

鉴于:

val df = Seq(
  (1, "fn", "red"),
  (2, "fn", "blue"),
  (3, "fn", "green"),
  (4, "aa", "blue"),
  (5, "aa", "green"),
  (6, "bb", "red"),
  (7, "bb", "red"),
  (8, "aa", "blue")
).toDF("id", "fn", "color")

进行计算:

val redOrNot = df.groupBy("fn")
  .agg(collect_set('color) as "values")
  .withColumn("hasRed", array_contains('values, "red"))

// gives null for no option
val colorPicker = when('hasRed, "red")
val result = df.join(redOrNot, "fn")
  .withColumn("resultColor", colorPicker) 
  .withColumn("color", coalesce('resultColor, 'color)) // skips nulls that leads to the answer
  .select('id, 'fn, 'color)

result看起来如下(这似乎是一个答案):

scala> result.show
+---+---+-----+
| id| fn|color|
+---+---+-----+
|  1| fn|  red|
|  2| fn|  red|
|  3| fn|  red|
|  4| aa| blue|
|  5| aa|green|
|  6| bb|  red|
|  7| bb|  red|
|  8| aa| blue|
+---+---+-----+

您可以链接 when运算符，并有一个默认值 otherwise .咨询 scaladoc of when operator .

我认为您可以使用窗口运算符或用户定义的聚合函数 (UDAF) 来做一些非常相似的事情(也许更有效)，但是……嗯……目前不知道如何去做。在这里留下评论以激励他人;-)

附言学到了很多!谢谢你的主意!