如何创建NSArray的NSArray

Question

I am trying to sort an array of NSDictionaries into an alphabatised array of arrays based of one of the NSDictionary valueForKey: first letters

effectively I want something that looks a little something like this

Array A // contains NSDictionaies with keyvalue MAF strings starting with A
 NSDictionary1
 NSDictionary2
 NSDictionary3
Array B // contains NSDictionaies with keyvalue MAF strings starting with B
 NSDictionary1
 NSDictionary2
 NSDictionary3
Array C // contains NSDictionaies with keyvalue MAF strings starting with C
 NSDictionary1
 NSDictionary2
 NSDictionary3
etc

So I have an array of Letters and inside each letter array I would like to have an Array of NSDictionary values that keyValue MAFs first letter should match.

So far I have an array of dictionaries that I have sorted like so

NSSortDescriptor *sortDescriptor;
        sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"MAF"
                                                      ascending:YES];
        NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];
        sortedDictionaryArray = [arrayData sortedArrayUsingDescriptors:sortDescriptors]; // use this in cellforrow: and didselectrow:

        NSLog(@"%@", sortedDictionaryArray); // this gives me a sorted array of NSdictionaries based off their MAF keyvalue.

This is what the NSDicitonary looks like

HADM = 1;
ISLOT = 0;
ISVERT = 0;
MAF = "Yazot"; // keyvalue I am trying to work with.

Then I get stuck, I am not sure where to go from here. if anyone could help me understand how to create an NSArray of NSArrays NSDictionaries that would be great! hopefully I have explained what I am trying to do correctly, if you need any more details just let me know and I will supply.

Answer 1

This code will first sort your array of dictionaries by using the objects assigned to the key @"MAF" . Than it will create a new Dictionary where it will add a mutable array for each first letter of that string and add the object to it.

NSArray *array = @[@{@"MAF": @"Yazot"}, @{@"MAF": @"Lorem"},@{@"MAF": @"Ipsum"}, @{@"MAF": @"Laura"},@{@"MAF": @"Isit"}];

NSArray *sortedArray = [array sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *obj1, NSDictionary *obj2) {
    return [obj1[@"MAF"] compare:obj2[@"MAF"]];
}];

NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];

for (NSDictionary *dict in sortedArray) {
    NSString *firstLetter = [dict[@"MAF"] substringToIndex:1];

    if(![[dictionary allKeys] containsObject:firstLetter])
        dictionary[firstLetter] = [NSMutableArray array];

    [dictionary[firstLetter] addObject:dict];

}

---

if you need case insensitive string handling, "L" and "l" should be put into the same array, do

NSArray *array = @[@{@"MAF": @"Yazot"}, @{@"MAF": @"Lorem"},@{@"MAF": @"Ipsum"}, @{@"MAF": @"Laura"},@{@"MAF": @"Isit"}];

NSArray *sortedArray = [array sortedArrayUsingComparator:^NSComparisonResult(NSDictionary *obj1, NSDictionary *obj2) {
    return [obj1[@"MAF"] caseInsensitiveCompare:obj2[@"MAF"]];
}];

NSMutableDictionary *dictionary = [NSMutableDictionary dictionary];

for (NSDictionary *dict in sortedArray) {
    NSString *firstLetter = [dict[@"MAF"] substringToIndex:1];
    firstLetter = [firstLetter lowercaseString];
    if(![[dictionary allKeys] containsObject:firstLetter])
        dictionary[firstLetter] = [NSMutableArray array];

    [dictionary[firstLetter] addObject:dict];

}

---

dictionary results in

{
    i =     (
                {
            MAF = Ipsum;
        },
                {
            MAF = Isit;
        }
    );
    l =     (
                {
            MAF = Laura;
        },
                {
            MAF = Lorem;
        }
    );
    y =     (
                {
            MAF = Yazot;
        }
    );
}

Answer 2

We can start by creating a dictionary of arrays of dictionaries.

NSMutableDictionary *dictsForFirstLetter = [[NSMutableDictionary alloc] init];

for (NSDictionary *dict in arrayData) {
    NSString *dictMAF = dict[@"MAF"];
    NSString *firstLetter = [[dictMAF substringToIndex:1] uppercaseString];
    NSMutableArray *dicts = dictsForFirstLetter[firstLetter];
    if (!dicts) {
        dicts = [[NSMutableArray alloc] init];
        dictsForFirstLetter[firstLetter] = dicts;
    }
    [dicts addObject:dict];
}

Then you can retrieve the array of dictionaries by the first letter of their MAF value:

NSArray *dicts = dictsForFirstLetter[@"Y"];

---

To get an alphabetized array from this, you can sort the dictionary's keys and enumerate over them:

NSMutableArray *alphabetizedDicts = [[NSMutableArray alloc] init];

NSArray *firstLetters = [dictsForFirstLetter allKeys];
NSArray *sortedFirstLetters = [firstLetters sortedArrayUsingSelector:@selector(caseInsensitiveCompare:)];

for (NSString *firstLetter in sortedFirstLetters) {
    NSArray *dicts = dictsForFirstLetter[firstLetter];
    [alphabetizedDicts addObject:dicts];
}