spark use underscore as parameter to RDD.flatmap or map

Question

Here is my data:RDD[Array[String]] in spark. And I want to count the sum of all the elements length in data.

For example, data:(Array(1,2),Array(1,2,3)). I want to get the sum: 2+3=5; At first, I use ：data.flatMap(_).count(),

Error :

error: missing parameter type for expanded function ((x$1) => data.flatMap(x$1))

But when I replace _ with x=>x and write: data.flatMap(x=>x).count(), it works. So I am confused by the _ . I think in scala _ can be referred as the actual parameter type, right?

Answer 1

Refer to the question here.

Essentially, _ itself does not define a function. It can be used as a placeholder for a variable name when used in the anonymous function syntax, but when used by itself it means nothing.