JS through the array, the array to achieve a weight (duplicate elements but one)

1. iterate method

It is the most simple array deduplication method (indexOf method)

Realization of ideas: a new array to traverse the array to be heavy, when a new value is not in the array (the indexOf -1) was added to the new array;

var arr=[2,8,5,0,5,2,6,7,2];
function unique1(arr){
  var hash=[];
  for (var i = 0; i < arr.length; i++) {
     if(hash.indexOf(arr[i])==-1){
      hash.push(arr[i]);
     }
  }
  return hash;
}

2. Analyzing Method array subscript

Call indexOf method, performance, and almost 1

Realization of ideas: if the current array of item i for the first time in the current array position i is not, then i represents the item is repeated, ignored. Otherwise, the result is stored in an array.

function unique2(arr){
  var hash=[];
  for (var i = 0; i < arr.length; i++) {
     if(arr.indexOf(arr[i])==i){
      hash.push(arr[i]);
     }
  }
  return hash;
}

3. Sort the adjacent removal method

Realization of ideas: to sort the array passed, after ordering the same value will be adjacent, then traverse an array after sorting, adding only new array does not overlap with the previous value.

function unique3(arr){
  arr.sort();
  var hash=[arr[0]];
  for (var i = 1; i < arr.length; i++) {
     if(arr[i]!=hash[hash.length-1]){
      hash.push(arr[i]);
     }
  }
  return hash;
}

4. iterate the optimization method (Reference)

Realization of ideas: double loop, outer loop represents from 0 to arr.length, the cycle represents the i + 1 to arr.length

Will not duplicate the right values into a new array. (Detected at a current cycle terminates when the outer loop repeats the same time into the value of the judgment)

function unique4(arr){
  var hash=[];
  for (var i = 0; i < arr.length; i++) {
    for (var j = i+1; j < arr.length; j++) {
      if(arr[i]===arr[j]){
        ++i;
      }
    }
      hash.push(arr[i]);
  }
  return hash;
}

5.ES6 achieve

The basic idea: ES6 provides a new data structure Set. It is similar to an array, but the value of the member is unique, no duplicate values.

Set function can accept an array (or array-like objects) as parameters, it is used to initialize.

function unique5(arr){
  var x = new Set(arr);
 return [...x];
}

Extended: If repeated, this element is removed

Array subscript deduplication

function unique22(arr){
  var hash=[];
  for (var i = 0; i < arr.length; i++) {
     if(arr.indexOf(arr[i])==arr.lastIndexOf(arr[i])){
      hash.push(arr[i]);
     }
  }
  return hash;
}