Filter array of objects into new array

Question

I have an array of objects that contains information for rows. I am trying to filter this information so that I get a new array containing each row value only once. So the following object would output an array like so ['1', '2', '3']

Here is my code. I am trying the map function but not sure if this is the right approach:

var myArray = [
    {
        "row": 1,
        "headline": "First Object"
    },
    {
        "row": 1,
        "headline": "Second Object"
    },
    {
        "row": 2,
        "headline": "Third Object"
    },
    {
        "row": 2,
        "headline": "Fourth Object"
    },
    {
        "row": 3,
        "headline": "Fifth Object"
    }
];
    
    var rows = myArray.map(function(row) {
        console.log(row)
    });

royhowie · Accepted Answer · 2014-10-30 02:04:42Z

1

The easiest way to do this would probably be to write all the properties to an object, then write them back to an array:

var o = {},
    uniqueArray = [];

myArray.forEach(function (d) {
    o[d.row] = true; // stores the key equal to d.row in the object
});
for (var k in o) {    // loop through all the keys in o
    if (o.hasOwnProperty(k))    // if the object o has that key
        uniqueArray.push(k);    // push it to the array
}
console.log(uniqueArray);
// ["1", "2", "3"];

answered Oct 30, 2014 at 2:04

royhowie

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Community · Accepted Answer · 2017-05-23 11:49:39Z

1

Put all the row values in an array...

var arrayAll = [];
for (var i = 0; i < myArray.length; i++) {
    arrayAll.push(myArray[i].row)
}

Then remove duplicates

var uniqueNames = [];
$.each(arrayAll, function (i, el) {
    if ($.inArray(el, uniqueNames) === -1) uniqueNames.push(el);
});

console.log(uniqueNames);

see this post for other options to remove duplicates, if you need a non JQuery option. Remove Duplicates from JavaScript Array

edited May 23, 2017 at 11:49

CommunityBot

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answered Oct 30, 2014 at 2:08

Urielzen

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1 Comment

Urielzen Over a year ago

I know, did you see the link that I added?

Lander Van Breda · Accepted Answer · 2014-10-30 02:25:42Z

1

For a more readable approach then the chosen answer I would go for :

var distinct = function(rows){
    var mappedValues = rows.map(function(single){
        return single.row;
    });
    return mappedValues.filter(function(item,pos){
        return mappedValues.indexOf(item) === pos;
    });
}

distinct(myArray);

Just my 2 cents.

answered Oct 30, 2014 at 2:25

Lander Van Breda

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4 Comments

royhowie Over a year ago

The only problem being that this is O(n^2). Large datasets will be extremely slow.

Lander Van Breda Over a year ago

@royhowie because I had the same thinking as you, so I made a jsperf to test it out as native functions or sometimes very good optimised. And i got a 3* speed increase against your function even with a larger dataset. jsperf.com/filter123

Lander Van Breda Over a year ago

@royhowie sorry I have to excuse myself, I made my test case with a large array copying the array didn't think about changing up the numbers. Your solution is indeed in big arrays the better solution.

royhowie Over a year ago

yeah, use Math.random()*10000 |0 and see what happens

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