Counting the occurrences / frequency of array elements

前端未结

关注

 30  2057

In Javascript, I\'m trying to take an initial array of number values and count the elements inside it. Ideally, the result would be two new arrays, the first specifying each

相关标签:

30条回答

梦毁少年i

2020-11-21 07:28

Check out the code below.

<html>
<head>
<script>
// array with values
var ar = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4];

var Unique = []; // we'll store a list of unique values in here
var Counts = []; // we'll store the number of occurances in here

for(var i in ar)
{
    var Index = ar[i];
    Unique[Index] = ar[i];
    if(typeof(Counts[Index])=='undefined')  
        Counts[Index]=1;
    else
        Counts[Index]++;
}

// remove empty items
Unique = Unique.filter(function(){ return true});
Counts = Counts.filter(function(){ return true});

alert(ar.join(','));
alert(Unique.join(','));
alert(Counts.join(','));

var a=[];

for(var i=0; i<Unique.length; i++)
{
    a.push(Unique[i] + ':' + Counts[i] + 'x');
}
alert(a.join(', '));

</script>
</head>
<body>

</body>
</html>

0 讨论(0)

忘了有多久

2020-11-21 07:29

Try this:

Array.prototype.getItemCount = function(item) {
    var counts = {};
    for(var i = 0; i< this.length; i++) {
        var num = this[i];
        counts[num] = counts[num] ? counts[num]+1 : 1;
    }
    return counts[item] || 0;
}

0 讨论(0)

梦毁少年i

2020-11-21 07:30
If using underscore or lodash, this is the simplest thing to do:
```
_.countBy(array);
```
Such that:
```
_.countBy([5, 5, 5, 2, 2, 2, 2, 2, 9, 4])
=> Object {2: 5, 4: 1, 5: 3, 9: 1}
```
As pointed out by others, you can then execute the _.keys() and _.values() functions on the result to get just the unique numbers, and their occurrences, respectively. But in my experience, the original object is much easier to deal with.
0 讨论(0)
发布评论:

提交评论
- 加载中...
暖寄归人

2020-11-21 07:31
If you are using underscore you can go the functional route
```
a = ['foo', 'foo', 'bar'];

var results = _.reduce(a,function(counts,key){ counts[key]++; return counts },
                  _.object( _.map( _.uniq(a), function(key) { return [key, 0] })))
```
so your first array is
```
_.keys(results)
```
and the second array is
```
_.values(results)
```
most of this will default to native javascript functions if they are available

demo : http://jsfiddle.net/dAaUU/
0 讨论(0)
发布评论:

提交评论
- 加载中...

离开以前

2020-11-21 07:31

Solution using a map with O(n) time complexity.

var arr = [2, 2, 2, 2, 2, 4, 5, 5, 5, 9];

const countOccurrences = (arr) => {
    const map = {};
    for ( var i = 0; i < arr.length; i++ ) {
        map[arr[i]] = ~~map[arr[i]] + 1;
    }
    return map;
}

Demo: http://jsfiddle.net/simevidas/bnACW/

0 讨论(0)

小蘑菇

2020-11-21 07:33

You can use an object to hold the results:

var arr = [5, 5, 5, 2, 2, 2, 2, 2, 9, 4];
var counts = {};

for (var i = 0; i < arr.length; i++) {
  var num = arr[i];
  counts[num] = counts[num] ? counts[num] + 1 : 1;
}

console.log(counts[5], counts[2], counts[9], counts[4]);

So, now your counts object can tell you what the count is for a particular number:

console.log(counts[5]); // logs '3'

If you want to get an array of members, just use the keys() functions

keys(counts); // returns ["5", "2", "9", "4"]

0 讨论(0)