原文鏈接
容器類常用的是數(shù)組字典，其實也能滿足大多數(shù)需要，但偶然看到對集合的需要，覺得集合很實用。

先定義一個函數(shù):把集合轉(zhuǎn)換為NSString

NSString *NSCollectionToString(id collection) {
    NSMutableString *result = [NSMutableString stringWithString:@"["];
    for (id obj in collection) {
        [result appendString:[obj description]];
        [result appendString:@", "];
    }
    //如果collection是非空集合
    if ([collection count] > 0) {
        NSInteger len = [result length];//獲取字符串的長度
        //去掉最后的,和空格
        [result deleteCharactersInRange:NSMakeRange(len -2, 2)];
        [result appendString:@"]"];
        return result;
    }
    //collection是空集合
    else {
        [result appendString:@"]"];
        return result;
    }
}

NSSet

//NSSet
- (void)aboutNSSet{
    [super viewDidLoad];
    //初始化NSSet,重復(fù)的元素不會被添加進去
    NSSet *set1 = [NSSet setWithObjects:@"王二",@"張三",@"李四",@"老五",@"王二", nil];
    NSLog(@"%ld",set1.count);
    NSLog(@"%@",NSCollectionToString(set1));
    
    //用集合初始化集合
    NSSet *set2 = [NSSet setWithSet:[NSSet setWithObjects:@"老五",@"王二", nil]];
    NSLog(@"%ld",set2.count);
    NSLog(@"%@",NSCollectionToString(set2));
    
    //拼接元素
    set1 = [set1 setByAddingObject:@"wangEr"];
    set1 = [set1 setByAddingObjectsFromSet:[NSSet setWithObjects:@"zhangSan",@"liSi", nil]];
    set1 = [set1 setByAddingObjectsFromArray:@[@"wangWu"]];
    NSLog(@"%@",NSCollectionToString(set1));
    NSLog(@"%ld",set1.count);
    
    //判斷兩個集合是否有交集
    BOOL intersect = [set1 intersectsSet:set2];
    BOOL equal = [set1 isEqualToSet:set2];
    BOOL subset = [set1 isSubsetOfSet:set2];
    NSLog(@"set2 是否包含 set1 %d",subset);
    NSLog(@"兩個集合是否相等%d",equal);
    NSLog(@"兩個集合是否有交集%d",intersect);
    
    //判斷集合是否包含某個元素
    BOOL contain = [set1 containsObject:@"xiaowu"];
    //判斷是否包含某個元素，并返回該元素或nil
    NSSet *s = [set1 member:@"wangEr"];
    NSLog(@"set1 是否包含 xiaowu %d",contain);
    NSLog(@"s 為 %@ ",s);
    
    //返回集合中的同一個元素，下面兩個結(jié)果一致，蘋果不保證絕對隨機
    NSLog(@"set1 中的隨機元素%@",[set1 anyObject]);
    NSLog(@"set1 中的隨機元素%@",[set1 anyObject]);
    
    //對set 中所有元素進行block處理，返回所有長度大于3的組成新數(shù)組
    NSSet *filterSet1 = [set1 objectsPassingTest:^BOOL(id  _Nonnull obj, BOOL * _Nonnull stop) {
        return (BOOL)([obj length] > 3);
    }];
    NSLog(@"set1中元素長度大于3的有%@",NSCollectionToString(filterSet1));

}

NSMutableSet

//NSMutableSet
- (void)aboutNSMutableSet{
    //初始化
    NSMutableSet *set = [NSMutableSet set];
    //添加元素
    [set addObject:@"wangEr"];
    [set addObjectsFromArray:@[@"zhangSan",@"liSi",@"wangWu"]];
    NSLog(@"添加元素后集合%@",NSCollectionToString(set));
    //從NSMutableSet中刪除元素
    [set removeObject:@"wangEr"];
    NSLog(@"刪除元素后的集合%@",NSCollectionToString(set));
    [set removeAllObjects];
    NSLog(@"清空后的集合%@",NSCollectionToString(set));
    
    //用新集合替換舊集合
    [set setSet:[NSSet setWithObjects:@"王二",@"張三", nil]];
    NSSet *set2 = [NSSet setWithObjects:@"李四",@"老五",@"王二", nil];
    //并集,交集，差集，調(diào)用者為NSMutableSet,但對數(shù)可為NSMutableSet/NSSet
    [set unionSet:set2];//并集
    NSLog(@"并集為%@",NSCollectionToString(set));
    [set minusSet:set2];//差集
    NSLog(@"差集為%@",NSCollectionToString(set));
    [set intersectSet:set2];//交集
    NSLog(@"交集為%@",NSCollectionToString(set));    
}

NSCountSet

- (void)aboutNSCountSet{
    
   //可計數(shù)集合繼承自NSMutableSet，所以它可以修改
    NSCountedSet *set = [NSCountedSet set];
    [set addObject:@"wangEr"];
    [set addObjectsFromArray:@[@"wangEr",@"zhangSan",@"liSi",@"laoWu"]];
    NSLog(@"%@",NSCollectionToString(set));
    NSLog(@"%ld",set.count); //4個元素
    
    //獲取元素出現(xiàn)的次數(shù)
    NSLog(@"wangEr 出再的次數(shù)是%ld",[set countForObject:@"wangEr"]);
    
    //刪除元素
    [set removeObject:@"wangEr"];
    NSLog(@"刪除 1 次 wangEr 后的集合是%@",NSCollectionToString(set));
    NSLog(@"刪除 1 次 wangEr 交數(shù)是%ld",[set countForObject:@"wangEr"]);
    [set removeObject:@"wangEr"];
    NSLog(@"刪除 2 次 wangEr 后的集合是%@",NSCollectionToString(set));
    NSLog(@"刪除 2 次 wangEr 交數(shù)是%ld",[set countForObject:@"wangEr"]);
  }

NSIndexSet

  NSMutableArray *bookArray=[NSMutableArray array];
  Book *book1=[Book bookWithName:@"chinese" price:19];
  Book *book2=[Book bookWithName:@"math" price:16];
  Book *book3=[Book bookWithName:@"english" price:15];
  [bookArray addObject:book1];
  [bookArray addObject:book2];
  [bookArray addObject:book3];

   //檢測判斷,返回第一個符合條件的數(shù)據(jù)索引
   NSUInteger pass = [bookArray indexOfObjectPassingTest:^BOOL(Book *obj, NSUInteger idx, BOOL * _Nonnull stop) {
                   if (obj.price > 25) {
                       return YES;
                   }else{
                       return NO;
                   }
                   
               }];
        if (pass == NSNotFound) {
            NSLog(@"notFound");
        }



   //檢測判斷,返回符合條件的數(shù)據(jù)索引集合        
   NSIndexSet *testSet =  [bookArray indexesOfObjectsPassingTest:^BOOL(Book* obj, NSUInteger idx, BOOL * _Nonnull stop) {
            
                if (obj.price> 15) {
                    return YES;
                }else{
                    return NO;
                }
              }];
        
        NSLog(@"%ld",testSet.count);
        [testSet enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL * _Nonnull stop) {
            NSLog(@"======%lu",idx);
        }];

NSOrderedSet

NSOrderSet 繼承自 NSObject
NSMutableOrderSet 繼承自 NSOrderSet
NSOrderedSet具有NSSet相似的功能，而NSMutableOrderedSet具有NSMutableSet相似的功能，
有增加、刪除、替換元素，排序，計算集合的交集、并集、差集等功能，同時有根據(jù)索引來對元素進行操作的功能

- (void)aboutOrderedSet{
    
    NSOrderedSet *orderSet = [NSOrderedSet orderedSetWithObjects:@"wangEr",@"zhangSan",@"liSi",@"laoWu", nil];
    NSLog(@"orderSet為%@",NSCollectionToString(orderSet));//有序
    //根據(jù)索引進行訪問
    NSLog(@"第一個元素是%@",[orderSet firstObject]);
    NSLog(@"第二個元素是%@",[orderSet objectAtIndex:1]);
    NSLog(@"最后一個元素是%@",[orderSet lastObject]);
    NSLog(@"(0-2)范圍內(nèi)的元素是%@",NSCollectionToString( [orderSet objectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 2) ]]));
    //用block返因長度 > 4 的元素索引
    NSIndexSet *indexSet = [orderSet indexesOfObjectsPassingTest:^BOOL(id  _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
        return (BOOL)([obj length]>4);
    }];
    NSLog(@"長度大于4的元素索引為%@",indexSet);
    
    
    //可變有序集合
    NSMutableOrderedSet *mutableOrderSet = [NSMutableOrderedSet orderedSet];
    [mutableOrderSet addObject:@"wangEr"];
    [mutableOrderSet addObjectsFromArray:[NSArray arrayWithObjects:@"wangEr",@"zhangSan",@"liSi",@"laoWu",nil]];
    //根據(jù)索引刪除元素
    [mutableOrderSet removeObjectAtIndex:2];
    NSLog(@"刪除第二個元素后的集合是%@",NSCollectionToString(mutableOrderSet));
    [mutableOrderSet removeObjectsAtIndexes:[NSIndexSet indexSetWithIndexesInRange:NSMakeRange(0, 1)]];
    NSLog(@"刪除第一個元素后的集合是%@",NSCollectionToString(mutableOrderSet));
    [mutableOrderSet removeObjectsInRange:NSMakeRange(0, 2)];
    NSLog(@"刪除兩個元素后的集合是%@",NSCollectionToString(mutableOrderSet));
}

NSSet如何判斷兩個元素是否相等？

同時滿足兩個條件
1.兩個對象通過isEqual:方法返回YES,即指針或內(nèi)容相等
2.兩個對象的hash方法返回值相等，即hashCode相等
但兩個對象內(nèi)容相等，但它們的hashCode不一定相等，
所以重寫父類的兩個方法
-(BOOL)isEqual:(id)object 和 - (NSInteger) hash

//不重寫父類方法的情況下系統(tǒng)會認為添加了5個不同的元素
 NSSet *set = [NSSet setWithObjects:
                      [[User alloc] initWithName:@"sun" pass:@"123"],
                      [[User alloc] initWithName:@"bai" pass:@"234"],
                      [[User alloc] initWithName:@"sun" pass:@"123"],
                      [[User alloc] initWithName:@"hu" pass:@"456"],
                      [[User alloc] initWithName:@"gan" pass:@"567"],
                      nil];

重寫繼承自NSObject的isEqual:

- (BOOL) isEqual:(id)object {
    if (self == object) {
        return YES;
    }
    if ([object class] == [self class]) {
        User *target = (User *) object;
        return [self.name isEqualToString:target.name] && [self.pass isEqualToString:target.pass];
    }
    return NO;
}

重寫繼承自NSObject的hash方法

- (NSInteger) hash { 
   NSInteger nameHash = (self.name == nil ? 0 : [self.name hash]); 
   NSInteger passHash = (self.pass == nil ? 0 : [self.pass hash]); 
   return nameHash * 31 + passHash; 
}