Compare the contents of two arrays and finding the differences - ios

Question

I have two arrays, one is an array from a fetch request of core-data (array1), the other is from data that is being pulled from the web(array2). What I want to do is compare array1 to array2 and any items that are in array2 that are not in array1 need to be added to core-data.
The data I'm pulling from has id's associated with each person. When I create a new "person" entity I save this id with it as well. I'm not sure how to compare the arrays using the Person's id, or even how to access that within an array.
Here is the fetch request:
NSFetchRequest *fetch = [[NSFetchRequest alloc] init];
NSError *error = nil;
[fetch setEntity:[NSEntityDescription entityForName:#"Person" inManagedObjectContext:self.managedObjectContext]];
NSSortDescriptor *sorter = [NSSortDescriptor sortDescriptorWithKey:#"Pid" ascending:YES];
request.sortDescriptors = #[sorter];
NSArray *items = [self.managedObjectContext executeFetchRequest:request error:&error];
I have the fetch sorted in the same way array2 with the new data is sorted. I'm just not sure how to compare the two and then add the new items into core-data. Please help?
Update:
NSDictionary *qDict = [JSON objectForKey:#"person"];
NSArray *qArry = [JSON objectForKey:#"person"];
//Used to print the id's
_testArray = [NSMutableArray arrayWithArray:[qDict valueForKey:#"id"]];
for (NSNumber *numb in _testArray) {
NSLog(#"id = %#", numb);
}
NSError *error = nil;
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Person"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"Pid IN %#", [qDict valueForKey:#"Pid"]];
[fetchRequest setPredicate:predicate];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"Pid" ascending:YES]]];
NSArray *items = [self.managedObjectContext executeFetchRequest:fetchRequest error:&error];
NSLog(#"%d how many items from the fetch", items.count);
for (NSDictionary *qdt in qArry) {
NSUInteger currentIndex = 0;
Person *q = nil;
if ([items count] > currentIndex) {
q = [items objectAtIndex:currentIndex];
}
if ([q.Pid integerValue] == [[qdt objectForKey:#"id"] integerValue]) {
// Either update the object or just move on
}
else {
// Add the object to core data
q = [NSEntityDescription insertNewObjectForEntityForName:#"Person" inManagedObjectContext:self.managedObjectContext];
q.url = [qdt valueForKey:#"url"];
q.Pid = [qdt objectForKey:#"id"];
q.text = [qdt valueForKey:#"personText"];
NSError *error = nil;
[_managedObjectContext save:&error];
}
currentIndex++;
}
//[_managedObjectContext save:&error];
}
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) {
UIAlertView *av = [[UIAlertView alloc] initWithTitle:#"Error retrieving data" message:#"Please try again" delegate:nil cancelButtonTitle:#"OK" otherButtonTitles:nil, nil];
[av show];
}];

Answer 1

First you can fetch the list of objects stored in your core data based on person's IDs that you retrieve from the web (idArray) and sort them based on the ID:
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:#"Person"];
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"id IN %#", idArray];
[fetchRequest setPredicate:predicate];
[fetchRequest setSortDescriptors:[NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:#"id" ascending:YES]]];
This will return you the list of objects that the id can also be found in the objects you retrieve from the web. Let us call this storedRecords array. Then you can do the following:
Set a counter,
Iterate over the downloadedArray (this is the array containing the objects retrieved from the web and it must be sorted by id too),
Use objectAtIndex in the storedRecords array,
Check the id of the storedManagedObject if it matches the id of the record object
if it does not match, it is a new object that you can save into core data. Otherwise, it is an existing object.
Increase the counter.
Here is an example:
int currentIndex = 0;
for (NSDictionary *record in downloadedArray) {
NSManagedObject *storedManagedObject = nil;
if ([storedRecords count] > currentIndex) {
storedManagedObject = [storedRecords objectAtIndex:currentIndex];
}
if ([[storedManagedObject valueForKey:#"id"] integerValue] == [[record valueForKey:#"id"] integerValue]) {
//this will be existing object in core data
//you can update the object if you want
} else {
//this will be new object that you can store into core data
}
currentIndex++;
}
This is similar to what is mentioned here:
http://www.raywenderlich.com/15916/how-to-synchronize-core-data-with-a-web-service-part-1

Answer 2

maybe you can do something like this:
NSMutableArray *webData = [NSMutableArray arrayWithObjects:#"object 1",#"object 2",#"object 3",#"object 4", nil];
NSMutableArray *coreData = [NSMutableArray arrayWithObjects:#"object 2",#"object 4", nil];
NSMutableArray *newData = [NSMutableArray arrayWithArray:webData];
[newData removeObjectsInArray:coreData];
//output "object 1", "object 3"
or if you have a custom NSObject inside the array and compare it with its primary key maybe you can do something like:
NSMutableArray *webData = [NSMutableArray arrayWithObjects:test1,test2,test3,test4, nil];
NSMutableArray *coreData = [NSMutableArray arrayWithObjects:test2,test3, nil];
__block NSMutableArray *newData = [NSMutableArray new];
[webData enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
__block testObject *object = (testObject *)obj;
__block BOOL isExisting = NO;
[coreData enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
testObject *innerObject = (testObject *)obj;
if(object._id == innerObject._id)
isExisting = YES;
}];
if(!isExisting)
[newData addObject:object];
}];
//output will be object 1 and object 4

Answer 3

Try this
NSMutableArray *array1 = [[NSMutableArray alloc] initWithObjects:#"a",#"a",#"a",#"d",#"b",#"b",#"c",#"a",#"c",nil];
NSMutableArray *array2 = [[NSMutableArray alloc] initWithObjects:[NSString stringWithFormat:#"%#",[array1 objectAtIndex:0]], nil];;
for(int i = 0;i<[array1 count];i++)
{
if ([array2 containsObject:[array1 objectAtIndex:i]]) {
NSLog(#"do nothing");
}
else{
[array2 addObject:[array1 objectAtIndex:i]];
NSLog(#"array2 is %#",array2);
}
NSLog(#"finally array2 is %#",array2);
}
array2 will be as { a,d,b,c }