Map Exercises

Those are all the basic methods of a map! Let's put this into implementation.

Most Popular Word

Write a function mostPopularWord() that takes an array of words (expect Strings) and returns the word that appears the most. This is known as most popular word.

So for example, using the following input:

var words = [
    "archive",
    "methodology",
    "database",
    "artificial intelligence",
    "Re-contextualized",
    "client-server",
    "reciprocal",
    "Inverse",
    "database",
    "Profit-focused",
    "regional",
    "maximized",
    "methodology",
    "Future-proofed",
    "radical",
    "initiative",
    "benchmark",
    "Universal",
    "methodology"
  ];

In this example, calling the mostPopularWord() function should return "methodology", because it appears 3 times, more than any other word in the List.

var answer = mostPopularWord(words);

console.log(answer); //Should print "methodology"

START HERE

(Hint🙈)

SOLUTION

Reverse Lookup

What happens if you don't have the key but have the value instead?

Getting a key based on the value is known as a reverse lookup, because instead of going from key -> value, you are going from value -> key.

You task is to write a function that takes a Map and a value, returning the corresponding key.

For example, given a map of state capitals, you should be able to call a reverse lookup (here, the function that does it is called "findStateForCapital") on the value "Denver", and the key "Colorado" will print to the console.

var stateCapitals = new Map()
                        .set("Alabama", "Montgomery")
                        .set("Alaska", "Juneau")
                        .set("Colorado", "Denver")
                        .set("Oregon", "Salem")
                        .set("Texas", "Austin")
                        .set("Virginia", "Richmond")
                        .set("Maryland", "Annapolis");

function findStateForCapital(capital) {
    //solve in here
}

var denverState = findStateForCapital("Denver")
console.log(denverState); //Should print Colorado

START HERE

(Hint🙈)

...

SOLUTION

SIDE NOTE

Be aware that in a Map, there may be multiple keys that share the same value.

For example, suppose you had a map of Phones to Manufacturers,

var map = new Map()
           .set("iPhone 5", "Apple")
           .set("Galaxy S4", "Samsung")
           .set("Lumia", "Nokia")
           .set("iPhone 7 Plus", "Apple")
           .set("iPhone 6", "Apple");

If you tried to do a reverse-lookup for "Apple", you will get multiple values. This is more complex than we're covering here, but it is an essential case to be aware of.