Repeated Characters in a String

Challenge.js

/**
 * Return the number of characters that are repeated in a given word/sentence
 */
// mine, with no big bells and whistles. Split the text and increase the count
// for each instance of the character. Tally everything above count of 1 and return.
function duplicateText( text ) {
  var counts  = {};
  var numDups = 0;

  text.split('').map(function( c ) {
    if ( counts[c] ) counts[c]++;
    else counts[c] = 1;
  });

  Object.keys( counts ).map(function( key ) {
    if ( counts[key] > 1 ) numDups++;
  });

  return numDups;
}

// clever regex
// Breaks down the text into an array, sorts it to bring all characters next to each other, then
// counts the matches it receives for characters repeated.
function duplicateCount(text){
  return (text.toLowerCase().split('').sort().join('').match(/(\w)\1+/g )||[]).length
}

// actually readable and clever
// This one rocks - it maps each character and checks that it exists at that index
// and that it ISN'T the last occurence of the character. Very clever use of .lastIndexOf()
function duplicateCount(text){
  text = text.toLowerCase()
  return text.split('').filter(function (c, i) {
    return text.indexOf(c) == i && text.indexOf(c) != text.lastIndexOf(c)
  }).length
}

// wtf...
function duplicateCount(text){
  return text.toLowerCase().split('').reduce(function(r, v){
    return r.c[v] = (r.c[v] || 0) + 1, r.t = r.t + (r.c[v] == 2), r;
  }, {c: {}, t: 0}).t;
}