Create an array of sub-arrays with the value of an element and the number of times it has repeated in JavaScript -

i'm trying take array (for example, array of years) , make new array of sub-arrays tells, firstly, unique element in original array and, secondly, how many time repeated.

for example, lets start of array of numbers [1999, 1999, 2000, 2005, 2005, 2005, 2015]

i function return array [[1999, 2], [2000, 1], [2005, 3], [2015, 1] ]
because year 1999 repeated twice, year 2000 was not repeated, year 2005 repeated 3 times, etc.

i can make new array removes duplicates, im getting weird behavior when comes making sub-arrays.

edit

here own faulty solution, in case wants point out did wrong.

var populateyearslist = function(yearsduplicate){  var uniqueyears = []; (var i=0; < yearsduplicate.length; i++){  if(uniqueyears.indexof(yearsduplicate[i]) == -1){   uniqueyears.push(yearsduplicate[i]) } else {   console.log("duplicate found") }; }  console.log (uniqueyears) }; 

i ran problem of trying change uniqueyears.push(yearsduplicate[i]) uniqueyears.push([ yearsduplicate[i], 1 ]) , trying replace console.log sort of incremented counter.

it easy as:

var input = [1999, 1999, 2000, 2005, 2005, 2005, 2015];  var uniq = []; input.foreach(function(n){     if (uniq.indexof(n)<0)          uniq.push(n); });  var output = uniq.map(function(n){     return [n, input.filter(function(m){ return m == n }).length] }); 

quick explanation how works

given input array, map its unique version new array mapping:

element ---> [ element, the number of occurrences in original array ]

edit note:: fixed previous solution might introduced duplicate element.