Scala 使用SparkSQL when函数选择列

在SparkSQL文档中，有一个when函数返回一列。给出的示例如下所示：

people.select(when(people("gender") === "male", 0)
   .when(people("gender") === "female", 1)
   .otherwise(2))

在本例中，when条件的结果为0、1或2。但是，如果我希望结果是people数据框的一列，该怎么办？例如，给定以下数据：

id | name    | gender | testosterone | estrogen
-----------------------------------------------
 1 | Joe     |   male |           10 |        2
 2 | Sue     | female |            3 |       12
 3 | John    |   male |            9 |        3
 4 | Kim     | female |            1 |       10

我想要这样的东西：

SELECT
    name,
    CASE WHEN gender = "male" THEN testosterone
         WHEN gender = "female" THEN estrogen
    END AS hormone_level
FROM
    people

结果是：

name    | hormone_level
-----------------------
Joe     |            10
Sue     |            12
John    |             9
Kim     |            10

只是

只是

when(people("gender") === "female", people("estrogen"))
  .when(people("gender") === "male", people("testosterone"))
  // .otherwise(???) Add base-case if required