CODEWITHSUNDEEP
scalascala-collections
stsatlantis
stsatlantis

Reputation: 555

Getting value from Hashmap with get or contains with apply method

Which one is better way to get values from a hashmap?

First Option:

val hm = HashMap(...)
if(hm.contains(keyWhichIsDefinitelyInTheKeys)){
  hm(keyWhichIsDefinitelyInTheKeys)  ... //do stuff
} else {
 ... //do stuff
}

Second Option:

hm.get(keyWhichIsDefinitelyInTheKeys) match {
    case Some => ...
    case None => ...
} // do stuff

Upvotes: 2

Views: 7910

Answers (3)

tg44
tg44

Reputation: 850

In performance:

There is a test code: http://pastebin.com/TbM82S7H

That is its output: http://pastebin.com/7An1DZw5

(cpu: i5 4590K)

None of the two call is better in performance...

Upvotes: 1

dk14
dk14

Reputation: 22374

This is better for some key:

 hm.getOrElse(key, defaultValue)

 //or

 hm.getOrElse(key, sys.error(s"unexpected key: $key"))

 //or more generally

 hm.get(key).map(v => doStuff(v)).getOrElse(doOtherStuff)

You can't be 100% sure that Map contains key, except some type-level protection (compile-time check); however, if you do then if won't help you eitherway, so just:

 hm(keyWhichIsDefinitelyInTheKeys)

Upvotes: 1

ccheneson
ccheneson

Reputation: 49410

As dk14 said, if you are not sure that the Map contains the key, you 'd better use get which return an Option.

You can use getOrElse to set a default value if the key is not present in the Map.

If you don't have a default value to set, you can use for comprehension if Option contains Some and not a None

scala> val hm = Map( 1 -> "Hello")
hm: scala.collection.immutable.Map[Int,String] = Map(1 -> Hello)

scala> for (i <- hm.get(2) ) { println(i) }

scala> for (i <- hm.get(1) ) { println(i) }
Hello

Upvotes: 3

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