I am encountering this : _* notation in many spark-scala answers, but couldn't find any documentation. What does it mean actually? An example of such usage is in the answer to this question
How to use DataFrame filter with isin in Spark Java?
line:
df.filter(col("something").isin(list: _*)
To understand it, lets take an example
scala> def echo(args: String*) =
for (arg <- args) println(arg)
echo: (args: String*)Unit
scala> val arr = Array("What's", "up", "doc?")
arr: Array[String] = Array(What's, up, doc?)
scala> echo(arr)
<console>:14: error: type mismatch;
found : Array[String]
required: String
echo(arr)
scala> echo(arr: _ *)
What's
up
doc?
This notation,arr:_* tells the compiler to pass each element of arr as its own argument to echo , rather than all of it as a single argument.