How to get unique values in an array

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How can I get a list of unique values in an array? Do I always have to use a second array or is there something similar to java\'s hashmap in JavaScript?

I am going

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一整个雨季

2020-11-22 14:37

Array.prototype.unique = function () {
    var dictionary = {};
    var uniqueValues = [];
    for (var i = 0; i < this.length; i++) {
        if (dictionary[this[i]] == undefined){
            dictionary[this[i]] = i;
            uniqueValues.push(this[i]);
        }
    }
    return uniqueValues; 
}

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野性不改

2020-11-22 14:38

Not native in Javascript, but plenty of libraries have this method.

Underscore.js's _.uniq(array) (link) works quite well (source).

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北荒

2020-11-22 14:38

I have tried this problem in pure JS. I have followed following steps 1. Sort the given array, 2. loop through the sorted array, 3. Verify previous value and next value with current value

// JS
var inpArr = [1, 5, 5, 4, 3, 3, 2, 2, 2,2, 100, 100, -1];

//sort the given array
inpArr.sort(function(a, b){
    return a-b;
});

var finalArr = [];
//loop through the inpArr
for(var i=0; i<inpArr.length; i++){
    //check previous and next value 
  if(inpArr[i-1]!=inpArr[i] && inpArr[i] != inpArr[i+1]){
        finalArr.push(inpArr[i]);
  }
}
console.log(finalArr);

Demo

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半阙折子戏

2020-11-22 14:42
These days, you can use ES6's Set data type to convert your array to a unique Set. Then, if you need to use array methods, you can turn it back into an Array:
```
var arr = ["a", "a", "b"];
var uniqueSet = new Set(arr); // {"a", "b"}
var uniqueArr = Array.from(uniqueSet); // ["a", "b"]
//Then continue to use array methods:
uniqueArr.join(", "); // "a, b"
```
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爱一瞬间的悲伤

2020-11-22 14:45

You only need vanilla JS to find uniques with Array.some and Array.reduce. With ES2015 syntax it's only 62 characters.

a.reduce((c, v) => b.some(w => w === v) ? c : c.concat(v)), b)

Array.some and Array.reduce are supported in IE9+ and other browsers. Just change the fat arrow functions for regular functions to support in browsers that don't support ES2015 syntax.

var a = [1,2,3];
var b = [4,5,6];
// .reduce can return a subset or superset
var uniques = a.reduce(function(c, v){
    // .some stops on the first time the function returns true                
    return (b.some(function(w){ return w === v; }) ?  
      // if there's a match, return the array "c"
      c :     
      // if there's no match, then add to the end and return the entire array                                        
      c.concat(v)}),                                  
  // the second param in .reduce is the starting variable. This is will be "c" the first time it runs.
  b);

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/some https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce

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猫巷女王i

2020-11-22 14:46

I was just thinking if we can use linear search to eliminate the duplicates:

JavaScript:
function getUniqueRadios() {

var x=document.getElementById("QnA");
var ansArray = new Array();
var prev;


for (var i=0;i<x.length;i++)
  {
    // Check for unique radio button group
    if (x.elements[i].type == "radio")
    {
            // For the first element prev will be null, hence push it into array and set the prev var.
            if (prev == null)
            {
                prev = x.elements[i].name;
                ansArray.push(x.elements[i].name);
            } else {
                   // We will only push the next radio element if its not identical to previous.
                   if (prev != x.elements[i].name)
                   {
                       prev = x.elements[i].name;
                       ansArray.push(x.elements[i].name);
                   }
            }
    }

  }

   alert(ansArray);

}

HTML:

<body>

<form name="QnA" action="" method='post' ">

<input type="radio"  name="g1" value="ANSTYPE1"> good </input>
<input type="radio" name="g1" value="ANSTYPE2"> avg </input>

<input type="radio"  name="g2" value="ANSTYPE3"> Type1 </input>
<input type="radio" name="g2" value="ANSTYPE2"> Type2 </input>


<input type="submit" value='SUBMIT' onClick="javascript:getUniqueRadios()"></input>


</form>
</body>

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