MergedMap.scala

/**
* Merging two maps keeping the first value if avaialble, otherwise second
*/
val map1 = Map("a"->Some(1), "b"->Some(3), "c"->None, "d"->None, "h"->Some(34))
val map2 = Map("a"->None, "b"->Some(11),  "c"->Some(22), "d"->None, "e"->Some(12), "f"->None)



// Option1
(map1.toList ++ map2.toList)
  .groupBy(_._1)
  .mapValues(_.flatMap(_._2).headOption)

// Option2
(map2 ++ map1).map{
  case (k,None) => k->map2.get(k).flatten
  case z => z
}

// Option 3
(map1.keys ++ map2.keys).map(k => k -> (map1.get(k) ++ map2.get(k)).flatten.headOption).toMap