优雅的获取数组最值、平均值（iOS）

应用场景（快速的获取数组最值、平均值）

- (void)valuesAboutArray{
    NSMutableArray *array = [NSMutableArray array];
    for (int i = 0; i < 10; i++) {
      CGFloat num = arc4random() % 100 + 1;
      [array addObject:[NSNumber numberWithFloat:num]];
    }
    CGFloat maxValue = [[array valueForKeyPath:@"@max.floatValue"] floatValue];
    CGFloat minValue = [[array valueForKeyPath:@"@min.floatValue"] floatValue];
    CGFloat avgValue = [[array valueForKeyPath:@"@avg.floatValue"] floatValue];
  }