How to check whether key or value exist in Map?

Question

I have a scala Map and would like to test if a certain value exists in the map.

myMap.exists( /*What should go here*/ )

Answer 1

There are several different options, depending on what you mean.

If you mean by "value" key-value pair, then you can use something like

myMap.exists(_ == ("fish",3)) myMap.exists(_ == "fish" -> 3) 

If you mean value of the key-value pair, then you can

myMap.values.exists(_ == 3) myMap.exists(_._2 == 3) 

If you wanted to just test the key of the key-value pair, then

myMap.keySet.exists(_ == "fish") myMap.exists(_._1 == "fish") myMap.contains("fish") 

Note that although the tuple forms (e.g. _._1 == "fish") end up being shorter, the slightly longer forms are more explicit about what you want to have happen.

Answer 2

Do you want to know if the value exists on the map, or the key? If you want to check the key, use isDefinedAt:

myMap isDefinedAt key 

Answer 3

you provide a test that one of the map values will pass, i.e.

val mymap = Map(9->"lolo", 7->"lala")
mymap.exists(_._1 == 7) //true
mymap.exists(x => x._1 == 7 && x._2 == "lolo") //false
mymap.exists(x => x._1 == 7 && x._2 == "lala") //true

The ScalaDocs say of the method "Tests whether a predicate holds for some of the elements of this immutable map.", the catch is that it receives a tuple (key, value) instead of two parameters.