iphone - 如何从 NSDictionary 中提取特定数据对于某些键具有相等的值到组合的 NSArray 中

Question

现在我有一个这样的字典，这只是一个例子，我有 A 到 Z:

(
        {
        id = 13;
        name = "Roll";
        firstLetter = R;
    },
        {
        id = 14;
        name = "Scroll";
        firstLetter = S;
    },
        {
        id = 16;
        name = "Rock";
        firstLetter = R;
    },
        {
        id = 17;
        name = "Start";
        firstLetter = S;
    }
)

我想提取具有相同 firstLetter 的字典并将它们组合成一个 NSArray 对象。预期结果如下:

R数组:

(
        {
        id = 13;
        name = "Roll";
        firstLetter = R;
    },
        {
        id = 16;
        name = "Rock";
        firstLetter = R;
    }
)

和S数组:

(

    {
        id = 14;
        name = "Scroll";
        firstLetter = S;
    },
        {
        id = 17;
        name = "Start";
        firstLetter = S;
    }
)

该怎么做？

Answer 1

我相信更好的方法是 Saohooou 建议的方法

但是可以优化为

NSArray *array = @[@{@"id": @13,@"name":@"Roll",@"firstLetter":@"R"},
                   @{@"id": @14,@"name":@"Scroll",@"firstLetter":@"S"},
                   @{@"id": @15,@"name":@"Rock",@"firstLetter":@"R"},
                   @{@"id": @16,@"name":@"Start",@"firstLetter":@"S"}];

NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];
[array enumerateObjectsUsingBlock:^(NSDictionary *dict, NSUInteger idx, BOOL *stop) {
    NSString *key = dict[@"firstLetter"];
    NSMutableArray *tempArray = dictionary[key];
    if (!tempArray) {
        tempArray = [NSMutableArray array];
    }
    [tempArray addObject:dict];
    dictionary[key] = tempArray;
}];
NSLog(@"%@",dictionary);