集合操作符

NSArray *array = @[@10, @20, @30, @40];
    
    //求和
    NSNumber *sum = [array valueForKeyPath:@"@sum.self"];
    NSLog(@"sum = %ld",sum.integerValue);
    
    //平均值
    NSNumber *avg = [array valueForKeyPath:@"@avg.self"];
    NSLog(@"avg = %ld",avg.integerValue);
    
    //元素个数
    NSNumber *count = [array valueForKeyPath:@"@count"];
    NSLog(@"count = %ld",count.integerValue);
    
    //最大值
    NSNumber *max = [array valueForKeyPath:@"@max.self"];
    NSLog(@"max = %ld",max.integerValue);
    
    //最小值
    NSNumber *min = [array valueForKeyPath:@"@min.self"];
    NSLog(@"min = %ld",min.integerValue);

对象操作符

NSArray *array = @[@"123", @"123", @"456", @"789", @"012"];
    
    //返回一个数组
    NSArray *arr1 = [array valueForKeyPath:@"@unionOfObjects.self"];
    NSLog(@"arr1 = %@",arr1);
    
    //返回一个去重的数组
    NSArray *arr2 = [array valueForKeyPath:@"@distinctUnionOfObjects.self"];
    NSLog(@"arr2 = %@",arr2);