How to access Map values in Scala

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is one of the shortest recipes, Recipe 11.17, “How to Access Map Values in Scala”

Problem

You want to access individual values stored in a map. You may have tried this and run into an exception when a key didn’t exist, and want to see how to avoid that exception.

Solution

Given a sample map:

scala> val states = Map("AL" -> "Alabama", "AK" -> "Alaska", "AZ" -> "Arizona")
states: scala.collection.immutable.Map[String,String] = Map(AL -> Alabama, AK -> Alaska, AZ -> Arizona)

Access the value associated with a key in the same way you access an element in an array:

scala> val az = states("AZ")
az: String = Arizona

However, be careful, because if the map doesn’t contain the requested key, a java.util.NoSuchElementException exception is thrown:

scala> val s = states("FOO")
java.util.NoSuchElementException: key not found: FOO

One way to avoid this problem is to create the map with the withDefaultValue method. As the name implies, this creates a default value that will be returned by the map whenever a key isn’t found:

scala> val states = Map("AL" -> "Alabama").withDefaultValue("Not found")
states: scala.collection.immutable.Map[String,String] = Map(AL -> Alabama)

scala> states("foo")
res0: String = Not found

Another approach is to use the getOrElse method when attempting to find a value. It returns the default value you specify if the key isn’t found:

scala> val s = states.getOrElse("FOO", "No such state")
s: String = No such state

You can also use the get method, which returns an Option:

scala> val az = states.get("AZ")
az: Option[String] = Some(Arizona)

scala> val az = states.get("FOO")
az: Option[String] = None

To loop over the values in a map, see the next recipe.

See Also

  • Recipe 11.21, “Testing for the Existence of a Key or Value in a Map”
  • Recipe 20.6, “Using the Option/Some/None Pattern” shows how to work with Option, Some, and None values

The Scala Cookbook

This tutorial is sponsored by the Scala Cookbook, which I wrote for O’Reilly:

You can find the Scala Cookbook at these locations:

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