数组作为value存入可变字典

//创建一个可变字典

NSMutableDictionary *dic = [NSMutableDictionary dictionary];

//遍历数组，将数组中的Student对象取出

for(Student *stu in student)

{

//取出班级名

NSString *class = stu.classNum;

//将class作为Key ，mArry 作为value 从可变字典中取出，看是否存在该数组

NSMutableArry *mArry = [dic objectForKey class];

//如果数组不存在，则创建数组

if(mArry == nil ){

mArry =[ [NSMutableArry alloc] init];

//将class作为key，mArry作为value 添加到可变字典中

[dic setValue:mArry forKey:class];

}

//将stu对象添加到数组中

[mArry addObject:stu];

}

NSLog(@“dic is %@“,dic);

//求每个班的平均分

for(NSString *class in dic)

{

NSInteger sum = 0;

NSArry *arry = [dic objectForKey class];

for(Student *stu in arry){

sum += stu.score;

}

NSLog(@“%@’s average is %.2f”,class,(float)sum / array.count);

}