List of lists as Map value does not compile

Question

I have in Scala a Map where the values are list of lists. I try to add a value with the following code:

var map = Map[String,List[List[String]]]()

val list1 = List ("A111", "B111")

var listInMap = map.getOrElse("abc", List[List[String]]())

listInMap += list1   // this line does not compile

map += ("abc" -> listInMap)

The problem is that in the line

listInMap += list1

it throws

type mismatch; found : List[String] required: String

. Why is String required if I need to add a list to the list? I need to add

list1

to

listInMap

Answer 1

listInMap += list1 is equivalent to listInMap = listInMap + list1. + operator is not defined in List for latest scala library (2.11.8) (marked deprecated in 2.7). So, + operator just concat the string values of listInMap and list1 with latest scala library.

For latest scala, you can use, listInMap = listInMap :+ list1

Also, check this: http://stackoverflow.com/a/7794297/1433665 as appending to list in scala has complexity of O(n)

List of lists as Map value does not compile

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