基本阵列比较算法

Question

我试图按照steps found here上比较两个数组，并知道何时创建新的对象，但我只是不明白它是如何工作的：

你最终两个已排序的数组 - 其中一个员工ID将 传递到提取请求中，另一个与管理对象匹配 他们。为了处理这些，你走路以下 步骤的有序列表：

Get the next ID and Employee. If the ID doesn't match the Employee ID, create a new Employee for that ID. 
Get the next Employee: if the IDs match, move to the next ID and Employee. 

不管你有多少个ID的传递，你只能执行单一的 取出，剩下的就是刚会走路的结果组。

基本上发生了什么是我有一个来自外部来源的对象ID数组，而客户端系统只有这些ID代表的对象的子集。我需要弄清楚我已经拥有哪些物品，如果我没有它们，请逐个创建它们。

我不明白这是如何工作的。我无法将其转换为代码：

for (int i =0;i<ids.count;i++) { 
    currentId = [ids objectAtIndex:i]; 
    currentObject = [objects objectAtIndex:i]; 

    if(currentObject.id != currentId) { 
     //create new object 
    } 

    //"get the next employee" 
    //uh what? 
    nextEmployee = [objects objectAtIndex:i+1]; //? 
    if(nextEmployee.id == currentId) { 
     //"move on to the next id" 
     continue; 
    } 
} 

我不明白这是怎么回事？我错过了什么？

Answer 1

尝试是这样的：

//Employee.h 
@property (nonatomic) NSInteger ID; 
@property (nonatomic, strong) NSString *name; 

//Employee.m 
@synthesize ID, name; 



//Place where you put algorithm 
#import "Employee.h" 
------------------------ 
NSMutableArray *employeeIDs = [NSArray arrayWithObjects:[NSNumber numberWithInt:123], [NSNumber numberWithInt:456], [NSNumber numberWithInt:789], nil]; 

//Creates employee objects 
Employee *employee1 = [[Employee alloc] init]; 
employee1.ID = 123; 
employee1.name = @"John Smith"; 

Employee *employee2 = [[Employee alloc] init]; 
employee2.ID = 456; 
employee2.name = @"Bob Day"; 

Employee *employee3 = [[Employee alloc] init]; 
employee3.ID = 789; 
employee3.name = @"Steve Jobs"; 

NSMutableArray *employeesArray = [NSArray arrayWithObjects:employee1, employee2, employee3, nil]; 

for (int index = 0; index <= [employeeIDs count]; index++) { 

    for(id currentEmployee in employeesArray){ 

     if(currentEmployee.ID != currentID){ 

      Employee *newEmployee = [[Employee alloc] init]; 
      newEmployee.name = [NSString stringWithFormat:@"Employee Name"]; 
      newEmployee.ID = 384; 

      [employeeIDs addObject:[NSNumber numberWithInteger:newEmployee.ID]]; 
      [employees addObject:newEmployee.name]; 

     } 
    } 
} 

希望这会有所帮助！

Answer 2

你需要在你的对象数组做线性搜索来检查，如果你能找到它，也许类似的东西：

for (int i = 0; i < ids.count; i++) { 
    bool found = NO; 
    currentId = [ids objectAtIndex:i]; 

    // We need to traverse the whole array to check if we can find the objectID somewhere... 
    for(int j = 0; j < objects.count; j++) { 
     currentObject = [objects objectAtIndex:j]; 

     if (currentId == currentObject) { 
      found = YES; 
      break; 
     } 
    } 

    if (!found) 
    { 
     // Create the new object 
    } 
} 

Answer 3

事情是这样的：

NSArray *wholeList = [[NSArray alloc]initWithObjects:@"employee1", @"employee2", @"employee3", @"employee4", @"employee5",@"employee6", nil]; 
NSArray *partialList = [[NSArray alloc]initWithObjects:@"employee2", @"employee13", @"employee7", nil]; 

for (id employeeID in partialList) //get one employee from the partialList 
{ 
    if (![wholeList containsObject:employeeID]) //check to see if it is in the wholeList 
    { 
     NSLog(@"This employee is not in the wholeList: %@", employeeID); 
     // do create new employee object for this employeeID, whatever... 
    } 
} 

Answer 4

在查看Core Data Programming Guide中的相同示例后，我发现此问题。

这是我的解决方案：

的关键是，你走2个数组分别，一个数组包含需要在核心数据存在的所有雇员字符串，另一个包含已经在核心存在Employee对象数据，由employeeId字符串过滤。这两个数组已经排序。

因此，可以说，我们有一个包含排序employeeIds字符串数组：

@"10",@"11",@"12",@"15",@"20" 

而且我们有一个包含有雇员10和2个Employee对象15

我们需要创建新的雇员matchingEmployees阵列对象为雇员ID为11,12和20的雇员，同时可能更新雇员10和15的属性。所以：

int i = 0; // employeeIds array index 
int j = 0; // matchingEmployees array index 

while ((i < [employeeIds count]) && (j <= [matchingEmployees count])){ 

    NSString *employeeId = [employeeIds objectAtIndex:i]; 

    Employee *employee = nil; 

    if ([matchingEmployees count]!=0) 
     employee = [matchingEmployees objectAtIndex:j]; 

    if (![employeeId isEqualToString:employee.employeeId]){ 

     employee = //Insert new Employee entity into context 
     employee.employeeId = employeeId; 

     //Set any attributes for employee that do not change 
    } 
    else { 
     //We matched employeeId to Employee so the next iteration 
     //of this loop should check the next Employee object 
     j++; 
    } 

    //Set any attributes for employee that change with each update 

    i++; 
}