Question

我们有一个应用程序调用SOAP Web服务并检索XML的长列表，然后应用程序将其解析为NSArray个NSDictionary个对象。 NSArray包含租赁公寓信息列表，每个信息都存储在NSDictionary中。

整个列表可能包含10种不同类型的公寓（即2室，3室），我们需要根据Room-Type将NSArray拆分为较小的NSArray，其中在NSDictionary个对象中有关键的“roomType”。

目前我们的算法是

使用[NSArray valueForKeyPath:@"@distinctUnionofObjects.room-type"] 获取一个独特的房间类型值列表。
循环显示唯一的房间类型值
对于每个唯一的房间类型值，使用NSPredicate从原始列表

我们的代码如下（为清晰起见重命名）：

NSArray *arrOriginal = ... ...; // Contains the Parsed XML list

NSMutableArray *marrApartmentsByRoomType = [NSMutableArray arrayWithCapacity:10];

NSMutableArray *arrRoomTypes = [arrOriginal valueForKeyPath:@"distinctUnionOfObjects.roomType"];

for(NSString *strRoomType in arrRoomTypes) {
  NSPredicate *predicateRoomType = [NSPredicate predicateWithFormat:@"roomType=%@", strRoomType];

  NSArray *arrApartmentsThatMatchRoomType = [arrOriginal filteredArrayUsingPredicate:predicateRoomType];  // TAKES A LONG TIME EACH LOOP-ROUND

  [marrApartmentsByRoomType addObject:arrApartmentsThatMatchRoomType];
}

然而，步骤3花费很长时间，因为原始列表可能包含大量（> 100,000）的项目。似乎NSPredicate遍历每个键值的整个列表。是否有更有效的方法可以根据NSArray密钥将较大的NSArray拆分为较小的NSDictionary？

Answer 1

如果您的分割数组的顺序不重要，我有一个解决方案：

NSArray *arrOriginal;
NSMutableDictionary *grouped = [[NSMutableDictionary alloc] initWithCapacity:arrOriginal.count];
for (NSDictionary *dict in arrOriginal) {
    id key = [dict valueForKey:@"roomType"];

    NSMutableArray *tmp = [grouped objectForKey:key];
    if (tmp == nil) {
        tmp = [[NSMutableArray alloc] init];
        [grouped setObject:tmp forKey:key];
    }
    [tmp addObject:dict];
}
NSMutableArray *marrApartmentsByRoomType = [grouped allValues];

Answer 2

这是非常高效的

- (NSDictionary *)groupObjectsInArray:(NSArray *)array byKey:(id <NSCopying> (^)(id item))keyForItemBlock
{
    NSMutableDictionary *groupedItems = [NSMutableDictionary new];
    for (id item in array) {
        id <NSCopying> key = keyForItemBlock(item);
        NSParameterAssert(key);

        NSMutableArray *arrayForKey = groupedItems[key];
        if (arrayForKey == nil) {
            arrayForKey = [NSMutableArray new];
            groupedItems[key] = arrayForKey;
        }
        [arrayForKey addObject:item];
    }
    return groupedItems;
}

Answer 3

改善@Jonathan回答

将数组转换为字典

维护与原始数组中相同的顺序

//only to a take unique keys. (key order should be maintained)
NSMutableArray *aMutableArray = [[NSMutableArray alloc]init];

NSMutableDictionary *dictFromArray = [NSMutableDictionary dictionary];

for (NSDictionary *eachDict in arrOriginal) {
//Collecting all unique key in order of initial array
NSString *eachKey = [eachDict objectForKey:@"roomType"];
if (![aMutableArray containsObject:eachKey]) {
    [aMutableArray addObject:eachKey];
}

NSMutableArray *tmp = [grouped objectForKey:key];
tmp  = [dictFromArray objectForKey:eachKey];

if (!tmp) {
    tmp = [NSMutableArray array];
    [dictFromArray setObject:tmp forKey:eachKey];
}
[tmp addObject:eachDict];

}

//NSLog(@"dictFromArray %@",dictFromArray);
//NSLog(@"Unique Keys :: %@",aMutableArray);

// 再次从字典转换为数组 ...

self.finalArray = [[NSMutableArray alloc]init];
for (NSString *uniqueKey in aMutableArray) {
   NSDictionary *aUniqueKeyDict = @{@"groupKey":uniqueKey,@"featureValues":[dictFromArray objectForKey:uniqueKey]};
[self.finalArray addObject:aUniqueKeyDict];
}

希望，当客户希望最终数组与输入数组的顺序相同时，它会有所帮助。

根据NSDictionary键值将NSArray拆分为子数组

3 个答案: