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Filter anagrams

importance: 4

Anagrams are words that have the same number of same letters, but in different order.

For instance:

nap - pan
ear - are - era
cheaters - hectares - teachers

Write a function aclean(arr) that returns an array cleaned from anagrams.

For instance:

let arr = ["nap", "teachers", "cheaters", "PAN", "ear", "era", "hectares"];

alert( aclean(arr) ); // "nap,teachers,ear" or "PAN,cheaters,era"

From every anagram group should remain only one word, no matter which one.

Open the sandbox with tests.

To find all anagrams, let’s split every word to letters and sort them. When letter-sorted, all anagrams are same.

For instance:

nap, pan -> anp
ear, era, are -> aer
cheaters, hectares, teachers -> aceehrst
...

We’ll use the letter-sorted variants as map keys to store only one value per each key:

function aclean(arr) {
  let map = new Map();

  for (let word of arr) {
    // split the word by letters, sort them and join back
    let sorted = word.toLowerCase().split('').sort().join(''); // (*)
    map.set(sorted, word);
  }

  return Array.from(map.values());
}

let arr = ["nap", "teachers", "cheaters", "PAN", "ear", "era", "hectares"];

alert( aclean(arr) );

Letter-sorting is done by the chain of calls in the line (*).

For convenience let’s split it into multiple lines:

let sorted = arr[i] // PAN
  .toLowerCase() // pan
  .split('') // ['p','a','n']
  .sort() // ['a','n','p']
  .join(''); // anp

Two different words 'PAN' and 'nap' receive the same letter-sorted form 'anp'.

The next line put the word into the map:

map.set(sorted, word);

If we ever meet a word the same letter-sorted form again, then it would overwrite the previous value with the same key in the map. So we’ll always have at maximum one word per letter-form.

At the end Array.from(map.values()) takes an iterable over map values (we don’t need keys in the result) and returns an array of them.

Here we could also use a plain object instead of the Map, because keys are strings.

That’s how the solution can look:

function aclean(arr) {
  let obj = {};

  for (let i = 0; i < arr.length; i++) {
    let sorted = arr[i].toLowerCase().split("").sort().join("");
    obj[sorted] = arr[i];
  }

  return Array.from(Object.values(obj));
}

let arr = ["nap", "teachers", "cheaters", "PAN", "ear", "era", "hectares"];

alert( aclean(arr) );

Open the solution with tests in the sandbox.