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Using jQuery, how can I iterate over an object, and get the unique values of a key with a count of each value?

For example, for this array:

var electrons = [
    { name: 'Electron1', distance: 1 }, 
    { name: 'Electron2', distance: 1 }, 
    { name: 'Electron3', distance: 2 }, 
    { name: 'Electron4', distance: 2 }, 
    { name: 'Electron5', distance: 2 }, 
    { name: 'Electron6', distance: 2 }, 
    { name: 'Electron7', distance: 2 }, 
    { name: 'Electron8', distance: 2 }, 
    { name: 'Electron9', distance: 2 }, 
    { name: 'Electron10', distance: 2 }, 
    { name: 'Electron11', distance: 3 }, 
];

I'd like to get back the following:

var distance_counts = {1: 2, 2: 8, 3: 1};

I've got this, which works but is a bit clumsy:

var radius_counts = {};
for (var i = 0; i < electrons.length; i++) { 
    if (electrons[i].distance in radius_counts) { 
         radius_counts[electrons[i].distance] += 1;
    } else { 
         radius_counts[electrons[i].distance] = 1;
    } 
}

Using jQuery, how can I iterate over an object, and get the unique values of a key with a count of each value?

For example, for this array:

var electrons = [
    { name: 'Electron1', distance: 1 }, 
    { name: 'Electron2', distance: 1 }, 
    { name: 'Electron3', distance: 2 }, 
    { name: 'Electron4', distance: 2 }, 
    { name: 'Electron5', distance: 2 }, 
    { name: 'Electron6', distance: 2 }, 
    { name: 'Electron7', distance: 2 }, 
    { name: 'Electron8', distance: 2 }, 
    { name: 'Electron9', distance: 2 }, 
    { name: 'Electron10', distance: 2 }, 
    { name: 'Electron11', distance: 3 }, 
];

I'd like to get back the following:

var distance_counts = {1: 2, 2: 8, 3: 1};

I've got this, which works but is a bit clumsy:

var radius_counts = {};
for (var i = 0; i < electrons.length; i++) { 
    if (electrons[i].distance in radius_counts) { 
         radius_counts[electrons[i].distance] += 1;
    } else { 
         radius_counts[electrons[i].distance] = 1;
    } 
}

• javascript
• jquery

Share Improve this question Follow edited Sep 7, 2012 at 13:26 Richard asked Sep 7, 2012 at 13:09 RichardRichard 65.6k135135 gold badges356356 silver badges570570 bronze badges 4

• Try this stackoverflow./questions/1960473/unique-values-in-an-array – Artem Vyshniakov Commented Sep 7, 2012 at 13:10
• 2 @Artem - That's a pletely different question about getting an array of unique values. – Richard Commented Sep 7, 2012 at 13:25
• Will the initial array always be sorted as is? – sp00m Commented Sep 7, 2012 at 13:39
• Would it be ok to use underscore.js? You could use _.pluck - although this will probably save you only one or two lines of code (and add the library....), a little like: jsfiddle/mYxVs – m90 Commented Sep 7, 2012 at 13:52

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 8

you could use map for this purpose as:

var distances = {};
$.map(electrons,function(e,i) {
   distances[e.distance] = (distances[e.distance] || 0) + 1;
});

or

var distances = {};
$.each(electrons,function(i,e) {
   distances[this.distance] = (distances[this.distance] || 0) + 1;
});

Also may I point out to you that although this code good to look and pact, this is not generally faster. Better make your code more faster and more easy to look at as:

var distances = {},e;
for (var i = 0,l=electrons.length; i < l; i++) { 
    e = electrons[i];
    distances[e.distance] = (distances[e.distance] || 0) + 1;
}

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