Javascript count duplicates and uniques and add to array

Question

I'm trying to count duplicates in an array of dates and add them to a new array.

But i'm only getting the duplicates and the amount of times they exist in the array.

What I want is:

[a, a, b, c, c] => [a: 2, b: 1, c: 2]

Code:

$scope.result = { };
    for(var i = 0; i < $scope.loginArray.length; ++i) {
        if(! $scope.result[$scope.loginArray[i]]){
             $scope.result[$scope.loginArray[i]] = 0;
        ++ $scope.result[$scope.loginArray[i]];}
    }

Any suggestions?

you just need to move this line out of if ++ $scope.result[$scope.loginArray[i]]; , otherwise the value not get updated on next iteration — Pranav C Balan
– Pranav C Balan, Commented Jun 7, 2016 at 9:10

Praveen Kumar Purushothaman · Accepted Answer · 2016-06-07 09:08:20Z

2

You might need an object for this, not an array. So what you are doing is already great, but the if condition is messing up:

$scope.result = {};
for (var i = 0; i < $scope.loginArray.length; ++i) {
  if (!$scope.result[$scope.loginArray[i]])
    $scope.result[$scope.loginArray[i]] = 0;
  ++$scope.result[$scope.loginArray[i]];
}

Snippet

var a = ['a', 'a', 'b', 'c', 'c'];
var r = {};
for (var i = 0; i < a.length; ++i) {
  if (!r[a[i]])
    r[a[i]] = 0;
  ++r[a[i]];
}
console.log(r);

Or in better way, you can use .reduce like how others have given. A simple reduce function will be:

var a = ['a', 'a', 'b', 'c', 'c'];
var r = a.reduce(function(c, e) {
  c[e] = (c[e] || 0) + 1;
  return c;
}, {});

console.log(r);

answered Jun 7, 2016 at 9:08

Praveen Kumar Purushothaman

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Comments

Jamiec · Accepted Answer · 2016-06-07 09:10:27Z

2

For that, you can use .reduce:

var arr = ['a','a', 'b', 'c', 'c'];
var result = arr.reduce(function(p,c){
  if(p[c] === undefined)
    p[c] = 0;
  p[c]++;
  return p;
},{});

console.log(result);

answered Jun 7, 2016 at 9:10

Jamiec

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Comments

Nenad Vracar · Accepted Answer · 2016-06-07 11:15:31Z

2

You can use reduce and return object

var ar = ['a', 'a', 'b', 'c', 'c'];
var result = ar.reduce(function(r, e) {
  r[e] = (r[e] || 0) + 1;
  return r;
}, {});

console.log(result)

You can also first create Object and then use forEach add properties and increment values

var ar = ['a', 'a', 'b', 'c', 'c'], result = {}
ar.forEach(e => result[e] = (result[e] || 0)+1);
console.log(result)

edited Jun 7, 2016 at 11:15

answered Jun 7, 2016 at 9:09

Nenad Vracar

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Comments

Gilad Artzi · Accepted Answer · 2016-06-07 09:11:25Z

1

lodash's countBy function will do the trick:

_.countBy(['a', 'a', 'b', 'c', 'c']) will evaluate to: {a: 2, b: 1, c: 2}

It does involve adding lodash as a dependency though.

answered Jun 7, 2016 at 9:11

Gilad Artzi

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2 Comments

Praveen Kumar Purushothaman Over a year ago

It would be better to use the native JavaScript functionality instead of using a library just for this, agree?

Gilad Artzi Over a year ago

You are 100% correct. I stated that it does involve adding a dependency, which can be a burden. Although lodash is a very small library and could be useful in many more cases.

Redu · Accepted Answer · 2016-06-07 10:24:30Z

0

I would do like this

var arr = ["a", "a", "b", "c", "c", "a"],
  red = arr.reduce((p,c) => (p[c]++ || (p[c]=1),p),{});
console.log(red);

answered Jun 7, 2016 at 10:24

Redu

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