利用KVC的方式更方便地获取数组中对象的属性的最值平均值等

直接上代码 输出结果也在相应的代码里标注出来了

 //main.m文件
 #import <Foundation/Foundation.h>
 #import "Student.h"

 int main(int argc, const char * argv[]) {
     @autoreleasepool {

         NSMutableArray <Student *> *_studentArrM;
         NSMutableArray <Student *> *_studentArrMTest;

         _studentArrM = [NSMutableArray array];
         _studentArrMTest = [NSMutableArray array];

         Student *s1 = [Student studentWithNum: chinese:90.0 math:96.0 english:100.0];
         Student *s2 = [Student studentWithNum: chinese:90.0 math:100.0 english:96.0];
         Student *s3 = [Student studentWithNum: chinese:100.0 math:90.0 english:96.0];

         [_studentArrM addObject:s1];
         [_studentArrM addObject:s2];
         [_studentArrM addObject:s3];

         double mathAvg = [[_studentArrM valueForKeyPath:@"@avg.math"]doubleValue];
         double mathMax = [[_studentArrM valueForKeyPath:@"@max.math"]doubleValue];
         double mathMin = [[_studentArrM valueForKeyPath:@"@min.math"]doubleValue];
         double mathSum = [[_studentArrM valueForKeyPath:@"@sum.math"]doubleValue];
         NSLog(@"数学平均分%f 数学最高分%f 数学最低分%f 所有人的数学总分%f",mathAvg,mathMax,mathMin,mathSum);

         /*
          输出的内容为：数学平均分95.333333 数学最高分100.000000 数学最低分90.000000 所有人的数学总分286.000000

          提示：有兴趣的话可以自己多测试几组数据
          */

         //接下来试着处理一下数组中的对象的是否有重复的问题
         //测试需要我们可以再次给可变数组添加一个重复的对象
         [_studentArrM addObject:s2];
         [_studentArrM addObject:s2];

         NSArray *arrDistinct = [_studentArrM valueForKeyPath:@"@distinctUnionOfObjects.num"];
         NSArray *arrUnion = [_studentArrM valueForKeyPath:@"@unionOfObjects.num"];

         NSLog(@"DistinctArray %@ \n UnionArray %@",arrDistinct,arrUnion);
         /*
          输出的内容为：
          DistinctArray (
          3,
          2,
          1
          )//提示：没有重复的所有值
          UnionArray (
          1,
          2,
          3,
          2,
          2
          )//提示：有重复的所有值
          */

         //为了处理 多个数组 中的重复值的情况再次添加一个一个对象到测试数组
         [_studentArrMTest addObject:s2];

         NSLog(@"%@",[@[_studentArrM,_studentArrMTest] valueForKeyPath:@"@distinctUnionOfArrays.num"]);
         NSLog(@"%@",[@[_studentArrM,_studentArrMTest] valueForKeyPath:@"@unionOfArrays.num"]);
         /*
          输出的内容为
          (3,
          2,
          1
          )//提示：没有重复的所有值

          (1,
          2,
          3,
          2,
          2,
          2
          )//提示：有重复的所有值

          */
     }
     return ;
 }

//Student.h文件
#import <Foundation/Foundation.h>

@interface Student : NSObject

/**
 学号
 */
@property (nonatomic,assign)int num;
/**
 语文成绩
 */
@property (nonatomic,assign)double chinese;
/**
 语文成绩
 */
@property (nonatomic,assign)double math;
/**
 语文成绩
 */
@property (nonatomic,assign)double english;

- (instancetype)initWithNum:(int)num chinese:(double)chinese math:(double)math english:(double)english;

+ (instancetype)studentWithNum:(int)num chinese:(double)chinese math:(double)math english:(double)english;

 1 //Student.m文件
 #import "Student.h"

 @implementation Student

 - (instancetype)initWithNum:(int)num chinese:(double)chinese math:(double)math english:(double)english{

     self = [super init];
     if(self){
         _num = num;
         _chinese = chinese;
         _math = math;
         _english = english;
     }
     return self;

 }

 + (instancetype)studentWithNum:(int)num chinese:(double)chinese math:(double)math english:(double)english{

     return [[Student alloc]initWithNum:num chinese:chinese math:math english:english];

 }

 @end