How to return an array from properties of an array of objects

Question

I have an array of objects as follows:

var lanes = [
{
 "name" : "Breakfast Special",
 "className" : "breakfast-special",
 "sales" : 200,
 "redemptions" : 137
},
{
 "name" : "Free Danish",
 "className" : "free-danish",
 "sales" : 300,
 "redemptions" : 237
},
{
 "name" : "Half Price Coffee",
 "className" : "half-price-coffee",
 "sales" : 240,
 "redemptions" : 37
}];

I want to create an array that contains only numerical values stored for 'redemptions'. I can access values as:

lanes[0].redemptions;

By going through each object using a loop, but I am looking for some efficient way to do that.

I tried this using map function as follows:

var arrayRedemptions = lanes.map(function () {return this.redemptions});

But it's not working. Any help would be appreciated.

Those are object literals, not "JSON objects". It is a fairly common misconception. — Useless Code
– Useless Code, Commented Aug 30, 2015 at 7:05

Satpal · Accepted Answer · 2015-08-30 06:30:42Z

2

You are quite close.

use

var arrayRedemptions = lanes.map(function(obj) {
    return obj.redemptions
});

answered Aug 30, 2015 at 6:30

Satpal

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5 Comments

akifquddus Over a year ago

Got it, the error was, I had some empty objects in the array. Fixed it like this: var arrayRedemptions = lanes.map(function(obj) { if (obj) { return obj.redemptions; } else { return -1; } });

Sherali Turdiyev Over a year ago

you just check: return obj && obj.redemptions

akifquddus Over a year ago

@SheraliTurdiyev Sorry didn't get your comment. What does that mean?

Sherali Turdiyev Over a year ago

no problem @user3130733. if obj equals undefined or null map returns it. It is for your prev comment(which is that: Got it, the error was). Also, i edited my answer

akifquddus Over a year ago

Perfect, Thanks!! @SheraliTurdiyev

Sherali Turdiyev · Accepted Answer · 2015-08-30 07:20:50Z

2

yeah. inside of map you can use these params(each item, index, array)

var arrayRedemptions = lanes.map(function (item, index, array) {
    return item ? item.redemptions : -1;
});

edited Aug 30, 2015 at 7:20

answered Aug 30, 2015 at 6:50

Sherali Turdiyev

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Comments

akifquddus · Accepted Answer · 2015-08-30 07:26:41Z

0

Just after adding extra check especially while working with Auto Generated Content:

var arrayRedemptions = array.map(function(obj) {
    if (obj) 
        return obj.redemptions;
    else
        return -1;
});

answered Aug 30, 2015 at 7:26

akifquddus

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