freeCodeCamp/curriculum/challenges/english/08-coding-interview-prep/rosetta-code/soundex.md

id	title	challengeType
5a23c84252665b21eecc8017	Soundex	5

Description

Soundex is an algorithm for creating indices for words based on their pronunciation. The goal is for homophones to be encoded to the same representation so that they can be matched despite minor differences in spelling (from the WP article). There is a major issue in many of the implementations concerning the separation of two consonants that have the same soundex code! According to the official Rules https://www.archives.gov/research/census/soundex.html. So check for instance if Ashcraft is coded to A-261.

• If a vowel (A, E, I, O, U) separates two consonants that have the same soundex code, the consonant to the right of the vowel is coded. Tymczak is coded as T-522 (T, 5 for the M, 2 for the C, Z ignored (see "Side-by-Side" rule above), 2 for the K). Since the vowel "A" separates the Z and K, the K is coded.
• If "H" or "W" separate two consonants that have the same soundex code, the consonant to the right of the vowel is not coded. Example: Ashcraft is coded A-261 (A, 2 for the S, C ignored, 6 for the R, 1 for the F). It is not coded A-226.

Write a function that takes a string as a parameter and returns the encoded string.

Instructions

Tests

tests:
  - text: <code>soundex</code> should be a function.
    testString: assert(typeof soundex == 'function', '<code>soundex</code> should be a function.');
  - text: <code>soundex("Soundex")</code> should return a string.
    testString: assert(typeof soundex("Soundex") == 'string', '<code>soundex("Soundex")</code> should return a string.');
  - text: <code>soundex("Soundex")</code> should return <code>"S532"</code>.
    testString: assert.equal(soundex("Soundex"), "S532", '<code>soundex("Soundex")</code> should return <code>"S532"</code>.');
  - text: <code>soundex("Example")</code> should return <code>"E251"</code>.
    testString: assert.equal(soundex("Example"), "E251", '<code>soundex("Example")</code> should return <code>"E251"</code>.');
  - text: <code>soundex("Sownteks")</code> should return <code>"S532"</code>.
    testString: assert.equal(soundex("Sownteks"), "S532", '<code>soundex("Sownteks")</code> should return <code>"S532"</code>.');
  - text: <code>soundex("Ekzampul")</code> should return <code>"E251"</code>.
    testString: assert.equal(soundex("Ekzampul"), "E251", '<code>soundex("Ekzampul")</code> should return <code>"E251"</code>.');
  - text: <code>soundex("Euler")</code> should return <code>"E460"</code>.
    testString: assert.equal(soundex("Euler"), "E460", '<code>soundex("Euler")</code> should return <code>"E460"</code>.');
  - text: <code>soundex("Gauss")</code> should return <code>"G200"</code>.
    testString: assert.equal(soundex("Gauss"), "G200", '<code>soundex("Gauss")</code> should return <code>"G200"</code>.');
  - text: <code>soundex("Hilbert")</code> should return <code>"H416"</code>.
    testString: assert.equal(soundex("Hilbert"), "H416", '<code>soundex("Hilbert")</code> should return <code>"H416"</code>.');
  - text: <code>soundex("Knuth")</code> should return <code>"K530"</code>.
    testString: assert.equal(soundex("Knuth"), "K530", '<code>soundex("Knuth")</code> should return <code>"K530"</code>.');
  - text: <code>soundex("Lloyd")</code> should return <code>"L300"</code>.
    testString: assert.equal(soundex("Lloyd"), "L300", '<code>soundex("Lloyd")</code> should return <code>"L300"</code>.');
  - text: <code>soundex("Lukasiewicz")</code> should return <code>"L222"</code>.
    testString: assert.equal(soundex("Lukasiewicz"), "L222", '<code>soundex("Lukasiewicz")</code> should return <code>"L222"</code>.');

Challenge Seed

function soundex (s) {
  // Good luck!
}

Solution

function soundex (s) {
  var a = s.toLowerCase().split('')
  var f = a.shift(),
    r = '',
    codes = {
       a: '', e: '', i: '', o: '', u: '',
       b: 1, f: 1, p: 1, v: 1,
       c: 2, g: 2, j: 2, k: 2, q: 2, s: 2, x: 2, z: 2,
       d: 3, t: 3,
       l: 4,
       m: 5, n: 5,
       r: 6
    };
  r = f + a
    .map(function(v, i, a) {
      return codes[v]
    })
    .filter(function(v, i, a) {
      return ((i === 0) ? v !== codes[f] : v !== a[i - 1]);
    })
    .join('');

  return (r + '000').slice(0, 4).toUpperCase();
}