如何修改spark dataframe行中的列值？

import org.apache.spark.sql.functions._
import org.apache.spark.sql.types._

val df = spark.createDataFrame(Seq(
  (1, "John", 25),
  (2, "Jane", 30),
  (3, "Bob", 35)
)).toDF("id", "name", "age")

val modifiedDF = df.withColumn("age", when(col("name") === "John", 26).otherwise(col("age")))

modifiedDF.show()

+---+----+---+
| id|name|age|
+---+----+---+
|  1|John| 26|
|  2|Jane| 30|
|  3| Bob| 35|
+---+----+---+