Hi i have NSArray of id objects.
And i know object description NSString.
how can i find object and avoid array enumeration?
p.s. i don't like to using NSDictionary, bcs it's do code more difficult
If this is a lookup you plan to perform more often and speed is an issue, you should probably not store the objects in a NSArray but instead in a NSDictionary to begin with, where the keys are the description strings of the objects and the values are the objects themselves. You can then use objectForKey: with the description string as argument, which is a O(1) lookup.
Try this one :
[myArray containsObject:yourObject];
Or you can filter it :
[myArray filterUsingPredicate:predicate];
Related
More for my interest than anything else.
If you have an Class defined like so...
MyClass
-------
NSString *name
And you put a lot of them into an array (or mutable array). Then you can use a predicate like this...
[NSPredicate predicateWithFormat:#"name = %#", someValue];
to filter the array so that it only contains objects whose names are the value given.
Or sort descriptor like so...
[NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES];
to sort the array by the name field in ascending order.
My question is, if you have an array of strings (or of NSNumbers) can you use similar "format" predicates?
Say for instance you had the array...
#[#"Cat", #"Bat", #"Dog", #"Cow"];
Could you use a "predicateWithFormat" to filter this array of a "sortDescriptorWithKey" to sort it?
I know you can use blocks but just wondering if this is possible?
Sure, you can filter an array of strings, or anything else, with predicateWithFormat:. As for sorting, you would use sortedArrayUsingSelector:, and use whichever selector you want (compare:, caseInsensitiveCompare:, etc.). There are no keys in a simple array, so you couldn't use sortDescriptorWithKey.
A string does not have any keys to use your predicates on or to sort by. You can find every other possible way to sort an array in the apple docs.
I want to be able to add objects to an NSArray and access them with Keys. Currently the way im doing it is creating a seperate NSDictionary of key-value pairs where the value is an integer number representing the index in my NSArray. This seems like an extra step to me.
If my understanding of NSDictionary is correct, only 'values' can be stored: a pointer to an object cannot.
Surely there must be an equivalent NSDictionary type function that allows objects to be stored and accessed with a key? I have looked through the documentation, but cant seem to find any answers, unless im missing something obvious.
NSDictionary is to store key value pairs. if you are adding key value pair after you created the dictioanry, use NSMutableDictionary class . example,
[dictionaryObject setObject:#"" forKey:#"abc"];
You can store objects in NSDictionary and can be accessed via keys...
In short, no.
An array (NSArray) is an ordered collection of references to objects, so simply said, an ordered collection of objects.
As opposed to dictionaries, which are unordered and values are accessed by keys.
You understanding of collections is probably wrong, you don't store values, but pointers (references).
The extra step is necessary if you need to store the references in an array, but in this case, you should consider using a dictionary. An option is to use keys that take care of the order.
For example :
[myDictionary objectForKey:#"1"];
could be an equivalent of :
[myArray objectAtIndex:1];
Thats wrong, you can store objects in a NSDictionary. Look at the method dictionaryWithObjects:forKeys: or dictionaryWithObjectsAndKeys:
I have no experience in Cocoa but looking at the documentation it seems like NSDictionary (or at least NSMutableDictionary) should handle your request (without you using NSArray).
I think I understand your problem. My suggestion for you is to use NSMutableArray and macros, like:
NSMutableArray *array=[[NSMutableArray alloc]init];
#define SOME_MACRO 0
id someObject;
[array insertObject:someObject atIndex:SOME_MACRO];
id getterObject=[array objectAtIndex:SOME_MACRO];
Of course define the macros in the header file.
So this is a rather basic question regarding the best way to sort an NSMutableArray of custom objects.
I have a an NSMutableArray of custom objects, each object with an NSString and NSDate that go together. I need to sort the array by the newest object (so latest NSDate), and I'm pretty sure I could simply use NSDate compare: NSDate if this was an array of just NSDate, but since I need all objects to be sorted and not just the date, I'm not sure if I can use that method.
In terms of pseudo-code, I need to: Look at individual object, determine if the current object's NSDate is the next biggest in the array, and if it is, move the object, not just the date.
Again, this is something I was even hesitant to ask since it's so basic but I don't want to go writing some grossly inefficient method if there is a pre-existing class method that will essentially do what I want, search an array of object's sub properties and sort the objects according to the subproperties.
Thanks for any help.
NSSortDescriptorss make this really simple. With NSMutableArray you can sort the existing array using sortUsingDescriptors: and with immutable arrays you create a new array using sortedArrayUsingDescriptors:
//This will sort by stringProperty ascending, then dateProperty ascending
[mutable_array sortUsingDescriptors:
#[
[NSSortDescriptor sortDescriptorWithKey:#"stringProperty" ascending:YES],
[NSSortDescriptor sortDescriptorWithKey:#"dateProperty" ascending:YES]
]];
This little snippet worked great for me:
[students sortUsingDescriptors:#[[NSSortDescriptor sortDescriptorWithKey:#"name" ascending:YES]]];
the code below is working, but I want to make sure it's correct. I'm nervous about having an empty Array inside my dictionary that I create from the plist, since typically it seems that if you don't, say, initWithCapacity:1 then you often get memory errors once you start trying to add items.
At least, that's been my experience with NSMutableDictionary. However, this is the first time I'm trying to implement nested data objects, so perhaps the reason this code works is that the nested array is automatically initialized when it's imported as part of its parent dictionary?
Any and all comments appreciated. Thanks.
First, here's what the plist looks like that I'm using to create my dictionary:
Next, here's my code where I'm using the plist to create a dictionary, then adding an item to dataArray
// Create a pointer to a dictionary
NSMutableDictionary *dictionary;
// Read "SomeData.plist" from application bundle
NSString *path = [[NSBundle mainBundle] bundlePath];
NSString *finalPath = [path stringByAppendingPathComponent:#"SomeData.plist"];
dictionary = [NSMutableDictionary dictionaryWithContentsOfFile:finalPath];
// Now let's see if we can successfully add an item to the end of this empty nested array. How 'bout the number 23
NSNumber *yetAnotherNumber = [NSNumber numberWithInt:23];
[[dictionary objectForKey:#"dataArray"] addObject:yetAnotherNumber];
// Dump the contents of the dictionary to the console
NSLog(#"%#", dictionary);
Okay, fine, simple, good. When I Log the dictionary contents it shows that "23" has been added as an array value to dataArray. So the code works. But again, I want to confirm that I'm not "getting lucky" here, with my code just happening to work even though I'm not properly initializing that nested array. If so, then I could run into unanticipated errors later on.
So to sum up, dataArray is an empty array inside the .plist, so do I need to initialize it somehow (using, for example initWithCapacity: or something else) before I can properly populate it, or is the way I'm coding here just fine?
Thanks again.
EDIT
Hey all. I've been doing continued research on this, in the interests of finding a satisfying answer. I think I may have stumbled upon something, via this link on deep copying. His previous posts on deep copying had presented some code to do essentially what I was looking for above: create a mutable copy of a dictionary or array, from a plist, that also has mutable sub-structures.
However, as mentioned in the link above, it looks like these methods were superfluous, due to the CFPropertyListCreateDeepCopy method, which can be invoked with a call such as
testData = CFPropertyListCreateDeepCopy(kCFAllocatorDefault, [NSDictionary dictionaryWithContentsOfFile:path], kCFPropertyListMutableContainersAndLeaves);
So, my question is, can I properly use CFPropertyListCreateDeepCopy, in the way shown, to achieve what I've been asking about here? In other words, can I use this method to import my dictionary from a plist with fully mutable, nested data objects?
As I mentioned in one of the comments, I know I can create a nested, mutable dictionary manually, but for complex data that's just not practical, and it seems unlikely that built-in methods to import a mutable plist don't exist. So, based on the above, it looks like I've possibly found the solution, but I'm still too new to this to be able to say for sure. Please advise.
(Side note: I would simply test the code, but as we've established, the current SDK is buggy with regard to allow you to edit immutable nested dictionaries, contrary to the documented behavior. So as before, I'm not just interested in whether this works, but whether it's correct)
Thanks in advance.
init... methods should only be called once, immediately after a call to alloc or allocWithZone:. When framework code creates and returns an object or graph of objects, their init... methods have already been called, so sending another init... message would have undefined results. Don't do that.
Interestingly, in spite of what the documentation appears to say (and admittedly I probably missed a key sentence or paragraph somewhere), when you create an instance of a mutable collection by reading a plist, any nested collections are also mutable. I ran the following little experiment in a test harness just to be sure:
NSMutableDictionary *pets = [NSMutableDictionary dictionaryWithContentsOfFile:#"/tmp/Pets.plist"];
NSMutableArray *cats = [pets objectForKey:#"cats"];
[cats addObject:#"Foo"]; // EDIT: Added line I accidentally omitted earlier
NSLog(#"%#", cats);
So again, the nested collections created when you read in the plist are fully initialized, and mutable to boot, so you can simply use them, as you've been doing.
EDIT
However, after doing some further reading of the docs, I think the OP is right to feel uneasy about relying on what is apparently an undocumented feature of the current version of the SDK. For example, the Property List Programming Guide states:
If you load the property list with
this call:
NSMutableArray * ma = [NSMutableArray arrayWithContentsOfFile:xmlFile];
ma is a mutable array with immutable
dictionaries in each element. Each key
and each value in each dictionary are
immutable.
So, to be on the safe side, if you need a nested collection to be mutable, you should create it yourself. For example, I'd recommend rewriting the code in the example above as follows:
NSMutableDictionary *pets = [NSMutableDictionary dictionaryWithContentsOfFile:#"/tmp/Pets.plist"];
NSArray *cats = [pets objectForKey:#"cats"];
NSMutableArray *mutableCats = [cats mutableCopy];
[pets setObject:mutableCats forKey:cats];
[mutableCats release];
You can then safely make changes to the nested mutable collection:
[mutableCats addObject:#"Foo"];
Any object in a dictionary which is created by reading from disk will be properly initialized. You will not have to do it on your own. However, as pointed out by jlehr, contents of the dictionary should be immutable. If you want the contents of the dictionary to be mutable, you will need to change them on your own. I have no idea why your program is not throwing an exception.
I do not know why you are getting memory errors while not using initWithCapacity:1 in other situations. The following code is perfectly valid:
NSMutableArray *array = [[NSMutableArray alloc] init];
[array addObject:#"object1"];
[array addObject:#"object2"];
NSLog(#"%#",array);
[array release];
If you don't specify a capacity, the array won't pre-allocate any memory, but it will allocate memory as required later.
Edit:
It is perfectly acceptable to use NSDictionary with CFPropertyListCreateDeepCopy. In Core Foundation, a CFPropertyList can be a CFDictionary, CFArray, CFNumber, CFString, or CFData. Since NSDictionary is toll-free bridged to CFDictionary, you can use it wherever a CFDictionary is asked for by casting, and vice-versa. Your code as is will give a warning, but you can suppress it by casting the dictionary and return values.
NSDictionary *testData = (NSDictionary*)CFPropertyListCreateDeepCopy(kCFAllocatorDefault, (CFDictionaryRef)[NSDictionary dictionaryWithContentsOfFile:path], kCFPropertyListMutableContainersAndLeaves);
I want an array which contains only unique items. I know I could do this with an NSDictionary adding items with keys and then get allKeys. This would ensure that the NSArray contains only unique items, but I feel that this would be overkill and believe that there should be an easier way to do this, but cannot find one.
NSArray* uniqueArray = [[NSSet setWithArray:originalArray] allObjects];
Uniqueness is based on the isEqual: method.
Use NSSet or NSMutableSet for this. Keep in mind that uniqueness will be based on object address if you don't override the isEqual: method. Unless, of course, you are using classes that implement that method (NSNumber, NSValue, for example).
You can use NSSet for this