removing duplicates from array in objective c

问题

I have an array with custom objects. Each array item has a field named "name". Now I want to remove duplicate entries based on this name value.

How should I go about achieving this.

Thanks in advance.

回答1:

You might have to actually write this filtering method yourself:

@interface NSArray (CustomFiltering)
@end

@implementation NSArray (CustomFiltering) 

- (NSArray *) filterObjectsByKey:(NSString *) key {
   NSMutableSet *tempValues = [[NSMutableSet alloc] init];
   NSMutableArray *ret = [NSMutableArray array];
   for(id obj in self) {
       if(! [tempValues containsObject:[obj valueForKey:key]]) {
            [tempValues addObject:[obj valueForKey:key]];
            [ret addObject:obj];
       }
   }
   [tempValues release];
   return ret;
}

@end

回答2:

I do not know of any standard way to to do this provided by the frameworks. So you will have to do it in code. Something like this should be doable:

NSArray* originalArray = ... // However you fetch it
NSMutableSet* existingNames = [NSMutableSet set];
NSMutableArray* filteredArray = [NSMutableArray array];
for (id object in originalArray) {
   if (![existingNames containsObject:[object name]]) {
      [existingNames addObject:[object name]];
      [filteredArray addObject:object];
   }
}

回答3:

I know this is an old question but here is another possibility, depending on what you need.

Apple does provide a way to do this -- Key-Value Coding Collection Operators.

Object operators let you act on a collection. In this case, you want:

@distinctUnionOfObjects

The @distinctUnionOfObjects operator returns an array containing the distinct objects in the property specified by the key path to the right of the operator.

NSArray *distinctArray = [arrayWithDuplicates valueForKeyPath:@"@distinctUnionOfObjects.name"];

In your case, though, you want the whole object. So what you'd have to do is two-fold: 1) Use @distinctUnionOfArrays instead. E.g. If you had these custom objects coming from other collections, use @distinctUnionOfArray.myCollectionOfObjects 2) Implement isEqual: on those objects to return if their .name's are equal

回答4:

I'm going to get flak for this...

You can convert your array into a dictionary. Not sure how efficient this is, depends on the implementation and comparison call, but it does use a hash map.

//Get unique entries
NSArray *myArray = @[@"Hello", @"World", @"Hello"];
NSDictionary *uniq = [NSDictionary dictionaryWithObjects:myArray forKeys:myArray];
NSLog(@"%@", uniq.allKeys);

---

*Note, this may change the order of your array.

回答5:

If you'd like your custom NSObject subclasses to be considered equal when their names are equal you may implement isEqual: and hash. This will allow you to add of the objects to an NSSet/NSMutableSet (a set of distinct objects).

You may then easily create a sorted NSArray by using NSSet's sortedArrayUsingDescriptors:method.

MikeAsh wrote a pretty solid piece about implementing custom equality: Friday Q&A 2010-06-18: Implementing Equality and Hashing

回答6:

If you are worried about the order

NSArray * newArray =
        [[NSOrderedSet orderedSetWithArray:oldArray] array]; **// iOS 5.0 and later** 

回答7:

It is quite simple in one line

NSArray *duplicateList = ... 

If you don't care about elements order then (unordered)

NSArray *withoutDUP1 = [[NSSet setWithArray:duplicateList] allObjects];

Keep the elements in order then (ordered)

NSArray *withoutDUP2 = [[NSOrderedSet orderedSetWithArray:duplicateList] array];

回答8:

Implement isEqual to make your objects comparable:

@interface SomeObject (Equality)
@end

@implementation SomeObject (Equality)

- (BOOL)isEqual:(SomeObject*)other
{
    return self.hash == other.hash;
}

- (NSUInteger)hash
{
    return self.name;///your case
}

@end

How to use:

- (NSArray*)distinctObjectsFromArray:(NSArray*)array
{
    return [array valueForKeyPath:@"@distinctUnionOfObjects.self"];
}

来源：https://stackoverflow.com/questions/4007427/removing-duplicates-from-array-in-objective-c