json jquery .. get value number of duplicate

Question

// for example
var arrayName = [1, 2, 2, 3, 4, 2];
alert ( arrayName[2].length ); // undefined

What I want is

alert ( arrayName[2].length ); // 3

Or any other way .. thank you

`arrayName[2]` (which means "3rd element of `arrayName` array") is a number `2`. A number doesn't have `length` property — zerkms, Jan 22 '14 at 22:14
@Pheonixblade9: it's more likely "not clear what you're asking". According to the "expected result" OP doesn't want just a number of unique elements, since it would be 4, not 3 — zerkms, Jan 22 '14 at 22:18

score 2 · Answer 1 · answered Jan 22 '14 at 22:18

2

To count the number of 2's in the array you can do

var instances = arrayName.filter(function(e) {
    return e===2;
}).length;

FIDDLE

answered Jan 22 '14 at 22:18

adeneo

312,895
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score 0 · Answer 2 · answered Jan 22 '14 at 22:15

0

You don't need a lenght. Just reference the value at that index:

alert(arrayName[2]);

answered Jan 22 '14 at 22:15

Bic

3,141
18
29

score 0 · Answer 3 · edited May 23 '17 at 10:25

0

Just add this to your array prototype and you can return a unique subset from the array:

Array.prototype.getUnique = function(){
   var u = {}, a = [];
   for(var i = 0, l = this.length; i < l; ++i){
      if(u.hasOwnProperty(this[i])) {
         continue;
      }
      a.push(this[i]);
      u[this[i]] = 1;
   }
   return a;
}

This is a duplicate of Unique values in an array

edited May 23 '17 at 10:25

Community

1
1

answered Jan 22 '14 at 22:15

Codeman

12,157
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1

-1 for plagiarism http://stackoverflow.com/a/1961068/251311 If you "borrow" a solution - be so kind to refer to the original author – zerkms Jan 22 '14 at 22:16
@zerkms I marked the question as duplicate and added a reference – Codeman Jan 22 '14 at 22:16

Tian Jin · Answer 4 · 2014-01-23T00:17:52.647

Apparently, you are mixing the concept of the index of an array with the actual element of that array.

In short, arrayName[2].length returns the length of the second element. The second element in this case is 2, its length being undefined.

While a good approach for achieving your goal is to use the library underscore:

arr = [1,2,2,2,3];

function countDuplicate(arr, dup) {
  return (_.filter(arr, function(num){ 
    return num == dup; 
  })).length;
}

console.log(countDuplicate(arr, 2));

The fiddle is available here.

json jquery .. get value number of duplicate

4 Answers4