dynamically create a column if a column in a spark dataframe if it does not already exist

addColumnIfDoesNotExist.scala

//An example of dynamically adding a column if it does not exist
val df = Seq(
  ("channel_one", "my_show", "episode1"),
  ("channel_one", "my_show", "episode2")
).toDF("network_name", "show_name", "episode")

//there is no rank column so add one
val newdf = df.columns match {
        case a if a contains "rank" => df
        case _ =>df.withColumn("rank", lit("0"))
}
newdf.show
// +------------+---------+--------+----+
// |network_name|show_name| episode|rank|
// +------------+---------+--------+----+
// | channel_one|  my_show|episode1|   0|
// | channel_one|  my_show|episode2|   0|
// +------------+---------+--------+----+

// there is a show_name column
val newdf2 = df.columns match {
        case a if a contains "show_name" => df
        case _ =>df.withColumn("rank", lit("0"))
}
newdf2.show
// +------------+---------+--------+
// |network_name|show_name| episode|
// +------------+---------+--------+
// | channel_one|  my_show|episode1|
// | channel_one|  my_show|episode2|
// +------------+---------+--------+