Sort object array using values from another array

Question

I have two arrays, both of objects.

Charities (unordered):

[{
    "_id": "5527c2b29a4c7ebe2953129d",
    "name": "Lorem ipsum",
    "number": 1,
    "metric": "Lorem ipsum",
    "metricConversion": 6,
    "logo": "http://api.fake.net/example.png",
    "country": "Albania",
    "twitter": "exampletwitter",
    "facebook": "examplefb"
}, ...]

Promotions:

[{
    "type": 1,
    "charity": "5527c2b29a4c7ebe2953129d",
    "start": Sun May 10 2015 14:11:32 GMT+0100 (BST),
    "end": Thu Jul 02 2009 00:00:00 GMT+0100 (BST),
    "priority": 10
}, ...]

The promotions array is ordered by the priority (greatest first).

What I am trying to do is order the charities array by the promotions array, so the charity with the highest value for priority is put first, etc (with the connection being _id to charity).

I can think of several easy ways to do this, however the ones that come to mind are very inefficient. Any suggestions?

Guffa · Accepted Answer · 2015-05-10 13:23:00Z

2

Create a map with the charity id as key and index (or priority) as value:

var map = {};
for (var i = 0; i < promotions.length; i++) {
  map[promotions[i].charity] = i;
}

Now you can sort the charities and use the map to determine their ordering:

charities.sort(function(a, b){
  return map[a._id] - map[b._id];
});

answered May 10, 2015 at 13:23

Guffa

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2 Comments

Benedict Lewis Over a year ago

map[a._id] - map[b._id] returns NaN if there isn't a promotion for one of the charities (presumably as map[..] is undefined)

Guffa Over a year ago

@BenedictLewis: Yes, that's right. I assumed that there were promotions for all the charities. If there aren't, then you need to decide how you want to sort the charities that doesn't have a charity.

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