How to extract specific data has equal value for some key from NSDictionary into a combined NSArray - iphone

Question

Right now i have a dictionary like this, it's just a example, i got A to 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;
}
)
I want to extract the dict has the same firstLetter and combine these into a NSArray object. The expected results like this:
R array:
(
{
id = 13;
name = "Roll";
firstLetter = R;
},
{
id = 16;
name = "Rock";
firstLetter = R;
}
)
and S array:
(
{
id = 14;
name = "Scroll";
firstLetter = S;
},
{
id = 17;
name = "Start";
firstLetter = S;
}
)
How to do that?

Answer 1

I believe the better method would be the one suggested by Saohooou
But it can be optimised as
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);

Answer 2

NSMutableDictionay *dic = [NSMutableDictionay dictionay];
for ( YourObject *obj in yourDic.allValues )
{
NSMutableArray *dateArray = dic[obj.firstLetter];
if ( !dateArray )
{
dateArray = [NSMutableArray array];
[dic setObject:dateArray forKey:obj.firstLetter];
}
[dateArray addObject:obj];
}
so dic is what you want

Answer 3

I assume you organized the dict as an NSArray.
NSMutableDictionary* result = [NSMutableDictionary dictionary]; // NSDictionary of NSArray
for (id entry in dict) {
NSString* firstLetter = [entry firstLetter];
// Find the group of firstLetter
NSMutableArray* group = result[firstLetter];
if (group == nil) {
// No such group --> create new a new one and add it to the result
group = [NSMutableArray array];
result[firstLetter] = group;
}
// Either group has existed, or has been just created
// Add the entry to it
[group addObject: entry];
}
result holds what you want.

Answer 4

try this
NSString *currentStr;
//this int is to detect currentStr
NSInteger i;
NSMutableArray* R_Array = [[NSMutableArray alloc] init];
NSMutableArray* S_Array = [[NSMutableArray alloc] init];
for (NSDictionary *myDict in MyDictArray){
NSString *tempStr = [myDict objectForKey:#"firstLetter"];
if(currentStr = nil && [currentStr isEqualToString:""]){
currentStr = tempStr;
if([currentStr isEqualToString:"R"] ){
[R_Array addObject:myDict];
i = 0;
}else{
[S_Array addObject:myDict];
i = 1;
}
}else{
if([currentStr isEqualToString:tempStr]){
(i=0)?[R_Array addObject:myDict]:[S_Array addObject:myDict];
}else{
(i=0)?[R_Array addObject:myDict]:[S_Array addObject:myDict];
}
}
}
Base on your dictionaries. There are only two type, so i just created two array and use if-else for solving the problem. if there are multy values, you can try switch-case to do it.
Lets do this
NSMutaleDictionary * speDict = [[NSMutableDictionary alloc] init];
for(i=0;i<26;i++){
switch (i){
case 0:
[speDict setObject:[NSMutableArray alloc] init] forKey:#"A"];
break;
case 1:
[speDict setObject:[NSMutableArray alloc] init] forKey:#"B"];
break;
Case 2:
[speDict setObject:[NSMutableArray alloc] init] forKey:#"C"];
break;
...........
Case 25:
[speDict setObject:[NSMutableArray alloc] init] forKey:#"Z"];
break;
}
}
for (NSDictionary *myDict in MyDictArray){
NSString *tempStr = [myDict objectForKey:#"firstLetter"];
switch (tempStr)
case A:
[self addToMySpeDictArrayWithObject:myDict andStr:temStr];
break;
case B:
[self addToMySpeDictArrayWithObject:myDict andStr:temStr];
break;
Case C:
[self addToMySpeDictArrayWithObject:myDict andStr:temStr];
break;
...........
Case Z:
[self addToMySpeDictArrayWithObject:myDict andStr:temStr];
break;
}
-(void)addToMySpeDictArrayWithObject:(NSDictionary*)_dict andStr:(NString*)_str
{
NSMutableArray *tempArray = [speDict objectForKey:_str];
[tempArray addObject:_dict];
}
then the speDict is like
A:
//all firstletter is A
myDict
myDict
myDict
B:
//all firstletter is B
myDict
myDict
.......

Answer 5

First of all the sample you've provided is an array of dicts (not a dict as the question notes). Now, the easiest way to query this array is by using an NSPredicate. Something like this perhaps:
NSArray *objects = ...; // The array with dicts
NSString *letter = #"S"; // The letter we want to pull out
NSPredicate *p = [NSPredicate predicateWithFormat:#"firstLetter == %#", letter];
NSArray *s = [objects filteredArrayUsingPredicate:p]; // All the 'S' dicts
If for some reason you need to group all of your objects without having to ask for a specific letter each time, you could try something like this:
// Grab all available firstLetters
NSSet *letters = [NSSet setWithArray:[objects valueForKey:#"firstLetter"]];
for (NSString *letter in letters)
{
NSPredicate *p = [NSPredicate predicateWithFormat:#"firstLetter == %#", letter];
NSArray *x = [objects filteredArrayUsingPredicate:p];
// Do something with 'x'
// For example append it on a mutable array, or set it as the object
// for the key 'letter' on a mutable dict
}
And of course you could further optimize this approach by implementing a method for filtering the array based on a letter. I hope that this makes sense.