在Objective-C中对自定义对象进行分组 [英] Grouping of Custom Objects in Objective-C

问题描述

我有Person类的自定义对象数组

  Person：NSObject {
 NSString * firstName; 
 NSString * lastName; 
 NSString * age; 
} 
 
 NSMutableArray * personsArray = [NSMutableArray array]; 
 Person * personObj1 = [[[Person alloc] init] autorelease]; 
 personObj1.firstName = @John; 
 personObj1.lastName = @Smith; 
 personObj1.age = @25; 
 [personsArray addObject：personObj1]; 
 
 Person * personObj2 = [[[Person alloc] init] autorelease]; 
 personObj2.firstName = @John; 
 personObj2.lastName = @Paul; 
 personObj2.age = @26; 
 [personsArray addObject：personObj2]; 
 
 Person * personObj3 = [[[Person alloc] init] autorelease]; 
 personObj3.firstName = @David; 
 personObj3.lastName = @Antony; 
 personObj3.age = @30; 
 [personsArray addObject：personObj3]; 
  

现在personsArray包含3个Person对象。

我们可以按照age或firstName等属性对这些对象进行分组吗？

我的预期结果是

  NSDictionary {
John=> {
 personObj1，//（因为personObj1 firstName是John）
 personObj2 //（因为personObj2 firstName John）
}，
David=> {
 personObj3，//（因为personObj3 firstName是David）
}，
} 
 
 
 
我知道我可以通过创建一个NSDictionary，然后通过personsArray迭代，然后检查每个第一个
  NSMutableDictionary * myDict = [NSMutableDictionary dictionary]; 
 
 for（Person * person in personsArray）{
 
 if（[myDict objectForKey：person.firstName]）{
 NSMutableArray * array = [myDict objectForKey：person 。名字]; 
 [array addObject：person]; 
 [myDict setObject：array forKey：person.firstName]; 
} else {
 NSMutableArray * array = [NSMutableArray arrayWithObject：person]; 
 [myDict setObject：array forKey：person.firstName]; 
} 
} 
 
 NSLog（@myDict％@，myDict）; 
 
 //结果myDict会给出所需的输出。 
  
但是有更好的方法吗？ 
 
 
 
如果我使用 @distinctUnionOfObjects ，我可以只分组字符串对象（不是这样的自定义对象。 
解决方案
 
 
 
 
感谢您的回答。 > 
 
 
 
  http：/ /stackoverflow.com/a/15375756/1190861  
 
 
 
您的案例中的代码如下：
  NSMutableDictionary * result = [NSMutableDictionary new]; 
 
 NSArray * distinctNames; 
 distinctNames = [personsArray valueForKeyPath：@@ distinctUnionOfObjects.firstName]; 
 for（NSString * name in distinctNames）{
 NSPredicate predicate = [NSPredicate predicateWithFormat：@firstName =％@，name]; 
 NSArray * persons = [personsArray filteredArrayUsingPredicate：predicate]; 
 [result setObject：persons forKey：name]; 
} 
 
 NSLog（@％@，result）; 
  
 
I have and array of custom objects of Person Class
Person : NSObject{
    NSString *firstName;
    NSString *lastName; 
    NSString *age;
}

NSMutableArray *personsArray = [NSMutableArray array];
Person  *personObj1 =  [[[Person alloc]  init] autorelease];
personObj1.firstName = @"John";
personObj1.lastName = @"Smith";
personObj1.age = @"25";
[personsArray addObject: personObj1];

Person  *personObj2 =  [[[Person alloc]  init] autorelease];
personObj2.firstName = @"John";
personObj2.lastName = @"Paul";
personObj2.age = @"26";
[personsArray addObject: personObj2];

Person  *personObj3 =  [[[Person alloc]  init] autorelease];
personObj3.firstName = @"David";
personObj3.lastName = @"Antony";
personObj3.age = @"30";
[personsArray addObject: personObj3];
Now personsArray contains 3 objects of Person objects.

Can we group this objects by attribute like age or firstName ?

My expected result is 
NSDictionary {
    "John" = >{
        personObj1, //(Its  because personObj1 firstName is John )
        personObj2 //(Its  because personObj2 firstName is John )
    },
    "David" = >{
        personObj3, //(Its  because personObj3 firstName is David )
    },
}
I know I can get this result by creating an NSDictionary and then Iterate through  personsArray, then check for each first
NSMutableDictionary *myDict = [NSMutableDictionary dictionary];

  for (Person *person in personsArray){

    if([myDict objectForKey: person.firstName]){
        NSMutableArray *array = [myDict objectForKey: person.firstName];
        [array addObject:person];
        [myDict setObject: array forKey:person.firstName];
    }else{
        NSMutableArray *array = [NSMutableArray arrayWithObject:person];
        [myDict setObject: array forKey:person.firstName];
    }
    }

    NSLog(@"myDict %@", myDict);

//Result myDict will give the desired output. 
But is there any better way to do ? 

If I am using  @distinctUnionOfObjects , I can group by string objects only (Not such custom objects. Am I right ?).

Thanks for the answer in advance.
解决方案
Checkout this answers it is very similar to what you want

http://stackoverflow.com/a/15375756/1190861

The code in your case will be as the following:
NSMutableDictionary *result = [NSMutableDictionary new];

NSArray *distinctNames;
distinctNames = [personsArray valueForKeyPath:@"@distinctUnionOfObjects.firstName"];
for (NSString *name in distinctNames) {
    NSPredicate predicate = [NSPredicate predicateWithFormat:@"firstName = %@", name]; 
    NSArray *persons = [personsArray filteredArrayUsingPredicate:predicate];
    [result setObject:persons forKey:name];
}

NSLog(@"%@", result);


                        
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