//第一種：利用NSDictionary的allKeys(allValues)方法。
    NSArray *array = @[@"2016-10-1",@"2016-10-9",
                  @"2016-10-9",@"2016-10-9",@"2016-12-25",
                  @"2016-12-25",@"2016-12-25",
                       @"2016-12-25",@"2016-12-25"];
    


    NSMutableDictionary *dic = [[NSMutableDictionary alloc]initWithCapacity:0];
    for (NSString *str in array) {
        
        [dic setValue:str forKey:str];
    }
    NSLog(@"%@",[dic allKeys]);<pre name="code" class="html">//列印結果
 (
    "2016-12-25",
    "2016-10-1",
    "2016-10-9"
)<pre name="code" class="html">
 

//第二種方法：利用NSSet的allObjects方法

    NSSet *set = [NSSet setWithArray:array];
    NSLog(@"%@",[set allObjects]);

<pre name="code" class="html">//第三種：利用陣列的containsObject
    NSMutableArray *ary = [[NSMutableArray alloc]init];
    for (NSString *str  in array) {
        if (![ary containsObject:str]) {
            [ary addObject:str];
        }
    }
    NSLog(@"%@",ary);
 

//第四種：利用keyValue

    array = [array valueForKeyPath:@"@distinctUnionOfObjects.self"];

NSLog(@"----%@",array);

    NSMutableArray *categoryArray = [[NSMutableArray alloc] init];
    for (unsigned i = 0; i < [array count]; i++){
        if ([categoryArray containsObject:[array objectAtIndex:i]] == NO){
            [categoryArray addObject:[array objectAtIndex:i]];
        }
        
    }
    
    NSLog(@"======%@",categoryArray);