I have something like this:
#interface Person : NSObject
{
NSString *fname;
NSString *lname;
}
NSString *keys = #"a","a","b","b","b"....";
for(NSString *key in keys)
{
Person *newPerson; //alloc new person
[myMutableDictionary setValue:newPerson forKey:key];
}
The above code will override the value with same key since NSDictionary doesn't allow duplicate keys. How can I do this?
I can do the above code by NSMutableArray, as in [array addObject:newPerson]; but it takes longer to fetch for (Key,value) as opposed to NSDictionary? My data is about 400,000 items, Any idea on how to do this efficiently? I need to load it once and do many fetches on it - No coreData, I tried it, its slow.
If you use an NSMutableArray as a key you can add multiple Person objects for the same key.
NSString *keys = #"a","a","b","b","b", ...;
for(NSString *key in keys)
{
Person *newPerson; //alloc new person
NSMutableArray *people;
if(!(people = [myMutableDictionary objectForKey:key]))
{
people = [NSMutableArray array];
[myMutableDictionary setValue:people forKey:key];
}
[people addObject:newPerson];
}
Related
i have 2 nsarrays
1 with nsdictionary's another with nsnumbers
NSArray *arr1 = #[#{#"id":#1},#{#"id":#2},#{#"id":#3},#{#"id":#4}];
NSArray *arr2 = #[#3,#1,#4,#2];
and i want to sort my arr1 through their id following the order of arr2
is this possible?
The problem with using sortedArrayUsingComparator: is you start dealing with O(n^2) lookup times. For each sort comparison in the first array, you have to do a lookup in the second array.
Your best bet is to take advantage of a hash table to reduce that to O(n) average complexity.
Your first step is to create a dictionary using id as a key. The result would look something like #{#1: #{#"id":#"1"}, ...}. Then you just have to construct an array by looping through arr3 and grabbing the values.
NSArray *arr1 = #[#{#"id":#1},#{#"id":#2},#{#"id":#3},#{#"id":#4}];
NSArray *arr2 = #[#3,#1,#4,#2];
NSMutableDictionary *map = [NSMutableDictionary dictionary];
for (NSDictionary *item in arr1) {
map[item[#"id"]] = item;
}
NSMutableArray *arr3 = [NSMutableArray array];
for (id key in arr2) {
[arr3 addObject:map[key]];
}
This solution of course assumes parity between the two arrays. If arr2 has an element not in arr1 it will crash when trying to add nil to arr3. If arr1 has a value not in arr2 it will be excluded from arr3. These are risks you will have to address based on your requirements.
Here is how you can do it by using a custom comparator:
NSArray* sorted= [arr1 sortedArrayUsingComparator: ^NSComparisonResult(NSDictionary *obj1, NSDictionary *obj2) {
return [arr2 indexOfObject:obj1[#"id"]] - [arr2 indexOfObject:[obj2[#"id"]];
}];
I exploited the fact that NSComparisonResult has +1 to represent an ascending order, -1 for descending and 0 to represent the same order.
- (NSArray*) sortedArray
{
NSArray *arr1 = #[#{#"id":#1},#{#"id":#2},#{#"id":#3},#{#"id":#4}];
NSArray *arr2 = #[#3,#1,#4,#2];
NSMutableArray *mutableArray = [NSMutableArray new];
for (NSNumber *number in arr2)
{
for (NSDictionary* dictionary in arr1)
{
NSNumber *number2 = dictionary[#"id"];
if ([number isEqual:number2])
{
[mutableArray addObject:dictionary];
break;
}
}
}
return mutableArray;
}
Hope someone could help me with that :
I'm using a NSDictionary to fill a UITableView.
Its model is like [key:userID => value:userName].
The tableView is only filled with userName but when clicked, it has to send the userID related.
The problem comes when I want to filter the UITable. I only found the way to filter a Dictionary by transforming it into NSArray (using Predicate) but it make me loose the relation between userNames and userIDs.
A solution would be to filter the initial NSDictionary to get a filtered NSDictionary (with still the relational key/value), but I don't know how to do that. I only found solutions to get Arrays.
How could I do that, or is there a better solution to do it?
There is a much better solution, François.
Create, from your NSDictionary (I will call it here myDictionary), an NSArray like this (declare it in your interface file):
NSArray *arrayForTableView;
Then, just after you load your NSDictionary, do the following:
arrayForTableView = [myDictionary allKeys]; // so you will have an array of all UserID's
Now, in your tableView: cellForRowAtIndexPath: method, you can do it like this:
cell.textLabel.text = [myDictionary objectForKey:[arraForTableView objectAtIndex:indexPath.row]];
And then, when you will want to pass the userID when the user selects the cell, in your tableView: didSelectRowAtIndexPath: you just do it this way:
id userIDSelected = [arraForTableView objectAtIndex:indexPath.row];
Then, when you want to filter the array according to the search, you can simply recreate your arrayForTableView, by "scanning" your NSDictionary this way:
NSString *typedString;
NSMutableArray *arrayFiltered = [NSMutableArray array];
for (int i = 0; i < [[myDictionary allKeys] count]; i++)
{
if ([[myDictionary objectForKey:[[myDictionary allKeys] objectAtIndex:i]] rangeOfString:typedString].location != NSNotFound)
{
[arrayFiltered addObject:[[myDictionary allKeys] objectAtIndex:i]];
}
}
arrayForTableView = arrayFiltered;
This way, you won't even need to change your UITableView dataSource and delegate methods.
You can do following to get value(userID) for selected key(userName) :
//iterate through whole dictionary
for(id key in yourNSDictionary)
{
// if key is the userName clicked
if([key isEqualToString:selectedUserName])
{
//userID for clicked userName
int userID = [yourNSDictionary objectForKey:#selectedUserName];
}
}
you're using an NSDictionary to populate an UITableView and this UITableView is only filled with the username which you get by doing
[dictionary objectForKey#"userID"];
a NSDictionary has two functions allkeys and allValues
NSArray* allUserID = [dictionary allKeys];
NSArray* allUserNames = [dictionary allValues];
this is a parallel arrays so that the index of one array, runs parallel with it's associated array.
Each cell of the table cell could also be a custom class that holds a reference to it's own id and username, this will allow you to only pass the cell and have it's data.
you can read about those functions in the NSDictionary documentation
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSDictionary_Class/Reference/Reference.html
i would recommend creating an NSArray or NSMutableArray with NSDictionary values - UITableViews are meant to be driven by arrays, where the array index matches the row number. Then you can easily create a custom filter for the array of dictionaries which take into account your data structure. Your code might include parts of this sample code:
NSString *idKey = #"userId";
NSString *nameKey = #"userName";
NSArray *arr = #[
#{
idKey : #(24),
nameKey : #"Oil Can Henry"
},
#{
idKey : #(32),
nameKey : #"Doctor Eggman"
},
#{
idKey : #(523),
nameKey : #"Sparticus"
},
];
NSString *searchTerm = #"Spar";
NSArray *newArray = [arr filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
return [evaluatedObject[nameKey] hasPrefix:searchTerm];
}]];
Advantages:
a single data structure to represent all your data
inherent, deterministic ordering
support for NSPredicate filtering
I have a dictionary with key-value pair populated from JSON returned data.What I wish to do is use the dictionary to populate UITableView.
I have this structure for table:
[Product Name]
By [Manufacturer Name]
What this means is that key is Product Name and Value is Manufacturer Name. I need to get the name of the key and the name of the value. How can this be done? and is it possible without for-loop?
I'd use the enumerateKeysAndObjectsUsingBlock: method. The following code builds a list of the strings you require.
NSMutableArray *names = [NSMutableArray array];
[dictionary enumerateKeysAndObjectsUsingBlock: ^(NSString *key, NSString *object, BOOL *stop) {
[names addObject[NSString stringWithFormat:#"%# By %#",key, object]];
}];
You can use the keyEnumerator of NSDictionary and for each key look up the value. This could look something like this:
for (NSString *p in dict)
{
NSString *m = [dict objectForKey:p];
// do something with (p,m)
}
You should not be concerned with avoiding for-loops. After all, something like a for loop will always happen somewhere underneath.
If your keys are dynamic from json then you can use
NSArray *keys = [dictionary allkeys];
Then in the table View Cell for row at index path method you can populate the table view with the corresponding keys and their values.
NSArray * keys = [results allKeys];
for (int i = 0;i<[keys count];c++){
NSString* productName = [key objectAtIndex:i];
NSString* manufacturerName = [results objectForKey:productName];
}
Hope this helps...
I have assumed the name as strings, you can change the type according to your situation..
We have an app that calls a SOAP web service and retrieves a long list of XML, which the app then parses into an NSArray of NSDictionary objects. The NSArray contains a list of Rental Apartment information, each of which is stored into an NSDictionary.
The entire list may contain 10 different types of Apartments (i.e. 2-room, 3-room), and we need to split the NSArray into smaller NSArrays based on Room-Type, which has the key "roomType" in the NSDictionary objects.
Currently our algorithm is
Use [NSArray valueForKeyPath:#"#distinctUnionofObjects.room-type"]
to obtain a list of unique room-type values.
Loop through the list of unique room-type values
For each unique room-type value, use NSPredicate to retrieve matching items from the Original list
Our code is below (renamed for clarity):
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];
}
However, step 3 is taking a long time as the original list may contain large amount (>100,000) of items. It seems that NSPredicate goes through the entire list for each key value. Is there a more efficient way of splitting a large NSArray into smaller NSArrays, based on NSDictionary keys?
If the order of your splited Arrays is not important, i have a solution for you:
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];
This is quite performant
- (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;
}
Improving #Jonathan answer
Converting array to dictionary
Maintaining the same order as it was in original array
//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);
//Converting from dictionary to array again...
self.finalArray = [[NSMutableArray alloc]init];
for (NSString *uniqueKey in aMutableArray) {
NSDictionary *aUniqueKeyDict = #{#"groupKey":uniqueKey,#"featureValues":[dictFromArray objectForKey:uniqueKey]};
[self.finalArray addObject:aUniqueKeyDict];
}
Hope, It will help when client wants final array in same order as input array.
NSMutableDictionary *expense_ArrContents = [[NSMutableDictionary alloc]init];
for (int i = 1; i<=4; i++) {
NSMutableArray *current_row = [NSMutableArray arrayWithObjects:#"payer_id",#"Expense_Type_id",#"Category_Id",#"SubCategory_Id",nil];
[expense_ArrContents setObject:current_row forKey: [NSNumber numberWithInt:i]];
}
NSArray *newArray = [expense_ArrContents allKeysForObject:#"payer_id"];
NSLog(#"%#",[newArray description]);
i want to get the list of key values containing the particular object which is in the array of values stored in nsmutabledictionary for a particular key.
In the line where you get all the keys ([expense_ArrContents allKeysForObject:#"payer_id"];) you actually get keys for an object that is not in any of the array's items. This #"player_id" is different object than the #"player_id" you added in current_row. In fact, maybe all of your rows have different #"player_id" objects (except if the compiler has made some optimization - maybe it threats that same string literal as one object instead of creating new object for each iteration).
Try creating an NSString object for the #"player_id" which you add to the current_row and then get all the keys for that same object:
NSString* playerId = #"player_id";
for(){
NSMutableArray *current_row = [NSMutableArray arrayWithObjects: playerId,...];
...
}
NSArray *newArray = [expense_ArrContents allKeysForObject:playerId];
Your NSArray *newArray = [expense_ArrContents allKeysForObject:#"payer_id"]; will not return any value because in expense_ArrContents there is no such key(#"payer_id"), instead there are keys like 1,2,3 etc.What is your requirement?Want to see what all keys are there in expense_ArrContents just log
NSArray*keys=[expense_ArrContents allKeys];
Try this :
NSMutableArray *array_key=[[NSMutableArray alloc]init];
for (NSString *key in expense_ArrContents) {
if ([[expense_ArrContents objectForKey:key] containsObject:#"payer_id"]) {
[array_key addObject:key];
}
}