Suppose I have list countries of type List[String] and map capitals of type Map[String, String]. Now I would like to write a function
pairs(countries:List[String], capitals:Map[String, String]):Seq[(String, String)]to return a sequence of pairs
(country, capital) and print an error if the capital for some country is not found. What is the best way to do that?
To start with, your Map[String,String] is already a Seq[(String,String)], you can formalise this a bit by calling toSeq if you wish:
val xs = Map("UK" -> "London", "France" -> "Paris")
xs.toSeq
// yields a Seq[(String, String)]
So the problem then boils down to finding countries that aren't in the map. You have two ways of getting a collection of those countries that are represented.
The keys method will return an Iterator[String], whilst keySet will return a Set[String]. Let's favour the latter:
val countriesWithCapitals = xs.keySet
val allCountries = List("France", "UK", "Italy")
val countriesWithoutCapitals = allCountries.toSet -- countriesWithCapitals
//yields Set("Italy")
Convert that into an error in whatever way you see fit.
countries.map(x=>(x, capitals(x)))
