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flatmapping a nested Map in scala

Suppose I have val someMap = Map[String -> Map[String -> String]] defined as such:

val someMap = 
Map( 
    ("a1" -> Map( ("b1" -> "c1"), ("b2" -> "c2") ) ),
    ("a2" -> Map( ("b3" -> "c3"), ("b4" -> "c4") ) ),
    ("a3" -> Map( ("b5" -> "c5"), ("b6" -> "c6") ) )   
)

and I would like to flatten it to something that looks like

List(   
    ("a1","b1","c1"),("a1","b2","c2"),
    ("a2","b3","c3"),("a2","b4","c4"),
    ("a3","b5","c5"),("a3","b6","c6")
)

What is the most efficient way of doing this? I was thinking about creating some helper function that processes each (a_i -> Map(String,String)) key value pair and return

def helper(key: String, values: Map[String -> String]): (String,String,String) 
= {val sublist = values.map(x => (key,x._1,x._2))
return sublist
}

then flatmap this function over someMap. But this seems somewhat unnecessary to my novice scala eyes, so I was wondering if there was a more efficient way to parse this Map.

Solution

  • No need to create helper function just write nested lambda:

    val result = someMap.flatMap { case (k, v) => v.map { case (k1, v1) => (k, k1, v1) } }

    Or

    val y = someMap.flatMap(x => x._2.map(y => (x._1, y._1, y._2)))