1NSArray *testArray = [NSArray arrayWithObjects:@"2.0", @"2.3", @"3.0", @"4.0", nil];

2 

3NSNumber *sum = [testArray valueForKeyPath:@"@sum.floatValue"];

4 

5NSNumber *avg = [testArray valueForKeyPath:@"@avg.floatValue"];

6 

7NSNumber *avg = [testArray valueForKeyPath:@"@max.floatValue"];

8 

9NSNumber *avg = [testArray valueForKeyPath:@"@min.floatValue"];

valueForKeyPath计算求和、平均值、最大、最小

在检索NSArray的时候，通常可以利用循环把里面的对象一个一个比较找出目标。另外也可以通过Key-Value的方法找出对象。

例如有下面这么一个Array:

(
{
city = “Beijing”;
country = “China”;
},
{
city = “Tokyo”;
country = “Japan”;
},
{
city = “New York”;
country = “U.S.”;
}
)

通常可以通过循环来找出对象，如下:

NSDictionary *resultDic = nil;
for(NSDictionary *dic in array){
if([[dic objectForKey:@"city"] isEqualToString:@”Beijing”] ){
resultsDic = [dic retain];
break;
}
}

也可以通过key-value的方法来搜索:

[array valueForKeyPath:@"city"];

上述代码会返回:

(
“Beijing”,
“Tokyo”,
“New York”
)

然后利用如下的代码获取array的index:

[[array valueForKeyPath:@"city"] indexOfObject:@”Beijing”];

然后用取得的index获取对象就可以:

[array objectAtIndex:[[array valueForKeyPath:@"city"] indexOfObject:@”Beijing]];

------------------------------------------------------------------------------------------------------------------------------------

NSMutableDictionary *dic=[NSMutableDictionary dictionary];

    [dic setObject:@"v1" forKey:@"k1"];

    [dic setObject:@"v2" forKey:@"k2"];

    [dic setObject:@"v3" forKey:@"k3"];

    

    NSArray *array=[NSArray arrayWithObjects:@"2",@"3",@"4",@"5",nil];

    

    [dic setObject:array forKey:@"k4"];

    id obj=[dic valueForKeyPath:@"[e-mail]"];

    NSLog(@"%@",[obj description]);//==14