Sort array of NSDictionaries by a value inside one of the keys

Question

I'm pulling an XML feed from a server, the feed contains train stations and their latitude and longitude locations.

I've managed to create an NSArray full of NSDictionary objects, each corresponding to a station.

In the dictionary there is a key for latitude and key for longitude. I also have a CLLocation object with the location of the device.

I know how to calculate the distance between the device and each station, but the distance isn't part of the dictionary. I would like to sort the array in order of distance from the device.

How would I do that? No idea where to start on this and Google or my books aren't being very helpful to me! Any help is much appreciated.

This post has the answer to your question: [http://stackoverflow.com/questions/805547/how-to-sort-an-nsmutablearray-with-custom-objects-in-it][1] [1]: http://stackoverflow.com/questions/805547/how-to-sort-an-nsmutablearray-with-custom-objects-in-it — Boon, Feb 27 '12 at 22:03
If anyone else is having a problem like this - make the array mutable, create a method using fast enumeration to add another field to each dictionary. Do the sort using blocks (as described in the link above) — Adam Waite, Feb 29 '12 at 13:19

score 10 · Accepted Answer · edited Nov 28 '14 at 05:11

10

Use the following;

NSArray *sortedArray;
sortedArray = [unsortedArray sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *first, NSDictionary *second) {
    // Calculate distances for each dictionary from the device
    // ...
    return [firstDistance compare:secondDistance];
}];

edited Nov 28 '14 at 05:11

answered Feb 27 '12 at 22:14

jrtc27

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score 3 · Answer 2 · edited Nov 27 '19 at 09:58

Unfortunately, you can't sort NSDictionary objects. You should create NSMutableArray and sort it instead.

See this - Collections Programming Topics - Sorting Arrays

Update: To sort array of dictionaries you can use for example this method of NSArray:

sortedArray = [someArray sortedArrayUsingFunction:compareElements context:NULL];

The compareElements function example:

NSInteger compareElements (id num1, id num2, void *context)
{
    int v1 = [[num1 objectForKey:@"distance"] integerValue];
    int v2 = [[num2 objectForKey:@"distance"] integerValue];
    if (v1 < v2)
        return NSOrderedAscending;
    else if (v1 > v2)
        return NSOrderedDescending;
    else
        return NSOrderedSame;
}

You can - he has an array of dictionaries. – jrtc27 Feb 27 '12 at 22:14 — jrtc27, Feb 27 '12 at 22:14

Sort array of NSDictionaries by a value inside one of the keys

2 Answers2