How to efficiently extract matching objects from an NSArray? [closed] - ios

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I'm looking for the most efficient way to achieve the following task...
I have an array of Objects of type Foo, amongst other properties, Foo has a latitude and a longitude property. Given an array of many Foo's, I need to extract the Foo's with matching lat / long's into one new array.
I have implemented several solutions which are working, including iterating using a for loop, and a solution using an NSPredicate, but both of these methods involve multiple iterations through an array. This array could potentially have hundreds of thousands of records, so i'm looking for something i can use which will achieve the desired result in one pass.
EDIT: Adding some pseudo-code to describe the approach i've already taken and to better describe the problem...
NSMutableArray * matchingLocations = [[NSMutableArray alloc] initWithCapacity:0];
for (Foo * checkingFoo in fooArray) {
NSMutableArray * checkingArray = [NSArray arrayWithArray:fooArray];
[checkingArray removeObject:checkingFoo];
for (Foo * foo in checkingArray) {
// I have a method coded for comparing two coordinates
if (checkingFoo.coordinate == foo.coordinate) {
[matchingLocations addObject:checkingFoo];
}
}
}

Answer 1

NSSet will provide a collection of unique objects. In order to implement it properly however you need to define what does mean to be identical for the Foo object. You do that in your Foo class implementation rewriting the method isEqual: and the method hash.
In your Foo class:
- (BOOL)isEqual:(id)object {
return (self.coordinate == [(Foo *)object coordinate]);
}
- (NSUInteger)hash {
return ([self.coordinate hash]);
}
Then everywhere in your code you can just use:
NSArray *array; // Your array with multiple Foo objects potentiually duplicates
NSSet *set = [NSSet setWithArray:array];
Have a loo kat the Apple Documentation reference for:
[NSObject isEqual:] https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intfm/NSObject/isEqual:
[NSSet setWithArray:]
https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSSet_Class/Reference/Reference.html#//apple_ref/occ/clm/NSSet/setWithArray:

Answer 2

You are running two fast enumeration as for loop of same array. Which is not correct. If you want to compare the co-ordinates then excecute for loop of different array. And also you can add directly to mutable array if same for loop only you are using.

Answer 3

If you want to compare objects from the array, then I suggest you use NSSet instead of NSArray.
It is very easy to use and the below link is something you want because I resolved such a case using NSMutableSet :
NSSet Tutorial