使用现有键将键值对添加到HashMap（Scala）

Question

I have a following HashMap

import collection.mutable.HashMap
val map = mutable.HashMap("key" -> mutable.HashMap("key" -> "value",
                                                    "key2" -> "value2"),
                          "key2" -> mutable.HashMap("key" -> "value",
                                                    "key2" -> "value2"))

How can I get the map look like

val map = mutable.HashMap("key" -> mutable.HashMap("key" -> "value",
                                                    "key2" -> "value2"),
                          "key2" -> mutable.HashMap("key" -> "value",
                                                    "key2" -> "value2",
                                                    "key3" -> "value3"),
                          "key3" -> mutable.HashMap("key" -> "value"))

In my head it would go something like this but I could not find a correct way.

map.get("key2").put("key3" -> "value3")
map.put("key3" -> ("key" -> "value3"))

Ultimately I want a structure which is easy to convert to Json

Answer 1

The put method does not work with parameters in the form of key -> value . You have to use + -operator. Also .get(key) returns an Option , so you have to .map on it:

map.get("key2").map(_ + "key3" -> "value3")
map += ("key3" -> mutable.HashMap("key" -> "value3"))

Also in the second line you need to explicitly create a HashMap otherwise it won't match the type of the map ( [String, HashMap] ).

This should answer you question, but Yuval Itzchakov is right, it might prove a good idea to use case classes and JSON serializer such as Jackson or Json4s , if you have a fixed structure for your objects.

Answer 2

You cannot use

map.get("key2").put("key3" -> "value3")

because it returns Option and it expects two parameters, not a tuple. You would need to unwrap value first by calling get and then call it like this:

map.get("key2").get.put("key3", "value3")

But there are simpler way to add new values to mutable map:

map("key3") = mutable.HashMap("key" -> "value", "key2" -> "value2") 
map("key2")("key3") = "value3"

// or 

map += ("key3" -> mutable.HashMap("key" -> "value", "key2" -> "value2"))
map("key2") += ("key3" -> "value3")