Is it possible to set a tag for an NSMutableArray? I have to somehow determine, in an array of arrays, the single array which needs to be rewritten, and if I could just set the tag to that inner array to 1 (or some other number), this would be extremely easy.
Example:
NSMutableArray* outerArray = [NSMutableArray new];
NSMutableArray* innerArray1 = [NSMutableArray new];
NSMutableArray* innerArray2 = [NSMutableArray new];
NSMutableArray* innerArray3 = [NSMutableArray new];
NSMutableArray* innerArray4 = [NSMutableArray new];
[outerArray addObject:innerArray1];
[outerArray addObject:innerArray2];
[outerArray addObject:innerArray3];
[outerArray addObject:innerArray4];
//now let's say innerArray1 needs to be rewritten
//I would like to be able to do this
[innerArray1 setTag:100];
//then later, when I need to determine which of the arrays inside outerArray
//needs to be rewritten, I can just do this
for(NSMutableArray* temp in outerArray) {
if(temp.tag == 100) {
//do what I need to do
}
}
But you can't use setTag: with NSMutableArrays. What would be a workaround?
Arrays are ordered collections, so why don't you just keep track of which index needs to be rewritten.
When something happens such that the array at index 0 (which, in your example, would be innerArray1) of outer array needs to be written, cache index 0 -- as a property if this routine needs to span across separate methods.
Then, when it comes time to do the rewrite, consult the cached index. Retrieve the array to be rewritten like this: NSArray *arrayToRewrite = [outerArray objectAtIndex:cachedIndexToRewrite]; Or access it directly: [[outerArray objectAtIndex:cachedIndexToRewrite] replaceObjectAtIndex:whatever withObject:whatever];
You could use an NSMutableDictionary instead. The "tag" would just be the key and the array would be the value.
Use associated objects. You can even add a category to NSMutableArray that would add a tag property to them.
#interface NSMutableArray (TagExtension)
#property (nonatomic, assign) NSInteger tag;
#end
#implementation NSMutableArray (TagExtension)
#dynamic tag;
static char TagExtensionKey;
-(NSInteger)tag {
NSNumber *ourTag = (NSNumber *)objc_getAssociatedObject(self, &TagExtensionKey);
if( ourTag ) {
return( [ourTag integerValue] );
}
return(0);
}
-(void)setTag:(NSInteger)newTag {
objc_setAssociatedObject(self, &TagExtensionKey, [NSNumber numberWithInteger:newTag], OBJC_ASSOCIATION_RETAIN);
}
#end
See also: How to add properties to NSMutableArray via category extension?
Not sure why a dictionary is a bad idea here… as alternatives, you can:
remember the index
or if each entry is a unique array, you can simply refer to it by pointer:
NSArray * tagged = theArray;
for (NSMutableArray * at in outerArray) {
if (tagged == at) {
//do what I need to do
}
}
Make your inner arrays class variables. Then you can just access them as:
for(NSMutableArray* temp in outerArray) {
if(temp == self.innerArray1) {
//do what I need to do
}
Related
It is clear from this question that there are many ways to remove duplicates from an NSArray when the array's elements are primitive types, or when the elements are perfect duplicates. But, is there a way to remove duplicates based on a transformation applied to each element, as is permitted in Underscore.js's uniq function, rather than by simply comparing the whole elements? And if a manual implementation would be difficult to optimize, is there an efficient system-provided method (or 3rd party library algorithm) for accomplishing this that I am missing?
A simple approach:
NSMutableArray* someArray = something;
for (int i = someArray.count - 1; i > 0; i--) {
MyObject* myObject = someArray[i];
for (int j = 0; j < i; j++) {
MyObject* myOtherObject = someArray[j];
if ([myObject isSortaEqual:myOtherObject]) {
[someArray removeObjectAtIndex:i];
break;
}
}
}
Yes, it's N-squared, but that's not a biggie unless the array is fairly large.
If you want to redefine what equality means for your objects, then consider overriding -hash and -isEqual:. Then you can create an NSSet from your array if order is irrelevant, or an NSOrderedSet if it is relevant. Here's an example of a Person class where I want the name of the person to determine object equality.
#interface Person
#property (nonatomic, copy) NSString *name;
#end
#implementation Person
- (BOOL)isEqual:(id)object
{
Person *otherPerson = (Person *)object;
return [self.name isEqualToString:otherPerson.name];
}
- (NSUInteger)hash
{
return [self.name hash];
}
#end
Uniquing them now is rather easy:
NSArray *people = ...;
// If ordered is irrelevant, use an NSSet
NSSet *uniquePeople = [NSSet setWithArray:people];
// Otherwise use an NSOrderedSet
NSOrderedSet *uniquePeople = [NSOrderedSet orderedSetWithArray:people];
Absolutely. You are looking for a way to pass your own method for testing for uniqueness (at least, that's what the uniq function you refer to does).
indexesOfObjectsPassingTest: will allow you to pass your own block to determine uniqueness. The result will be an NSIndexSet of all the objects in the array that matched your test. With that you can derive a new array. The block you are passing is roughly equivalent to the Underscore iterator passed to uniq.
The sister method, indexesOfObjectsWithOptions:passingTest: also allows you to specify enumeration options (i.e. concurrent, reverse order, etc.).
As you mention in your question, there are lots of ways to accomplish this. NSExpressions with blocks, Key-value coding collections operators, etc. could be used for this as well. indexesOfObjectsPassingTest: is probably the closest to what you seem to be looking for, though you can do much the same thing (with a lot more typing) using expressions.
I just came up against this problem, so I wrote a category on NSArray:
#interface NSArray (RemovingDuplicates)
- (NSArray *)arrayByRemovingDuplicatesAccordingToKey:(id (^)(id obj))keyBlock;
#end
#implementation NSArray (RemovingDuplicates)
- (NSArray *)arrayByRemovingDuplicatesAccordingToKey:(id (^)(id obj))keyBlock
{
NSMutableDictionary *temp = [NSMutableDictionary dictionaryWithCapacity:[self count]];
for (NSString *item in self) {
temp[keyBlock(item)] = item;
}
return [temp allValues];
}
#end
You can use it like this (this example removes duplicate words, ignoring case):
NSArray *someArray = #[ #"dave", #"Dave", #"Bob", #"shona", #"bob", #"dave", #"jim" ];
NSLog(#"result: %#", [someArray arrayByRemovingDuplicatesAccordingToKey:^(id obj){
return [obj lowercaseString];
}]);
Output:
2015-02-17 17:44:10.268 Untitled[4043:7711273] result: (
dave,
shona,
jim,
bob
)
The 'key' is a block that returns an identifier used to compare the objects. So if you wanted to remove Person objects according to their name, you'd pass ^(id obj){ return [obj name]; }.
This solution is O(n), so is suitable to large arrays, but doesn't preserve order.
How does one create a NSSet of objects from an array based on a property.
e.g. Array of objects, each with a strong reference to a type property, and multiple occurrences of each type exist in the array. How can this be turned into an NSSet holding a single object of each type.
NSSet *distinctSet = [NSSet setWithArray:[array valueForKeyPath:#"#distinctUnionOfObjects.property"]];
A dictionary essentially has this functionality already. Its keys are a set, so you can create the dictionary to hold the objects, keyed by whatever attribute you're interested in:
[NSDictionary dictionaryWithObjects:arrayOfObjects
forKeys:[arrayOfObjects valueForKey:theAttribute]];
If you ask the dictionary for allValues now, you have only one object for each attribute. I should mention that with this procedure, the later objects will be kept in favor of earlier. If the order of your original array is significant, reverse it before creating the dictionary.
You can't actually put those objects into an NSSet, because the NSSet will use the objects' isEqual: and hash methods to determine whether they should be members, rather than the key attribute (of course, you can override these methods if this is your own class, but that would likely interfere with their behavior in other collections).
If you really really feel that you need a set, you will have to write your own class. You can subclass NSSet, but conventional wisdom is that composition of Cocoa collections is far easier than subclassing. Essentially, you write a class which covers any set methods you're interested in. Here's a (quite incomplete and totally untested) sketch:
#interface KeyedMutableSet : NSObject
/* This selector is performed on any object which is added to the set.
* If the result already exists, then the object is not added.
*/
#property (assign, nonatomic) SEL keySEL;
- (id)initWithKeySEL:(SEL)keySEL;
- (id)initWithArray:(NSArray *)initArray usingKeySEL:(SEL)keySEL;
- (void)addObject:(id)obj;
- (NSArray *)allObjects;
- (NSArray *)allKeys;
- (BOOL)containsObject:(id)obj;
- (NSUInteger)count;
-(void)enumerateObjectsUsingBlock:(void (^)(id, BOOL *))block;
// And so on...
#end
#import "KeyedMutableSet.h"
#implementation KeyedMutableSet
{
NSMutableArray * _objects;
NSMutableSet * _keys;
}
- (id)initWithKeySEL:(SEL)keySEL
{
return [self initWithArray:nil usingKeySEL:keySEL];
}
- (id)initWithArray:(NSArray *)initArray usingKeySEL:(SEL)keySEL
{
self = [super init];
if( !self ) return nil;
_keySEL = keySEL;
_objects = [NSMutableArray array];
_keys = [NSMutableSet set];
for( id obj in initArray ){
[self addObject:obj];
}
return self;
}
- (void)addObject:(id)obj
{
id objKey = [obj performSelector:[self keySEL]];
if( ![keys containsObject:objKey] ){
[_keys addObject:objKey];
[_objects addObject:obj];
}
}
- (NSArray *)allObjects
{
return _objects;
}
- (NSArray *)allKeys
{
return [_keys allObjects];
}
- (BOOL)containsObject:(id)obj
{
return [_keys containsObject:[obj performSelector:[self keySEL]]];
}
- (NSUInteger)count
{
return [_objects count];
}
- (NSString *)description
{
return [_objects description];
}
-(void)enumerateObjectsUsingBlock:(void (^)(id, BOOL *))block
{
for( id obj in _objects ){
BOOL stop = NO;
block(obj, &stop);
if( stop ) break;
}
}
#end
NSMutableSet* classes = [[NSMutableSet alloc] init];
NSMutableSet* actualSet = [[NSMutableSet alloc] init];
for(id object in array) {
if([classes containsObject:[object class]] == NO) {
[classes addObject:[object class]];
[actualSet addObject:object];
}
}
You would use:
NSSet* mySetWithUniqueItems= [NSSet setWithArray: yourArray];
This should work regardless of the type of objects in your array and would populate the NSSet with only one occurence of any duplicate objects in your array.
I hope this helps.
Update:
Next best thing: is use concatenation of class name and object property first then use the above method.
self.concatenatedArray=[NSMutableArray arrayWithCapacity:4];
for (TheClass* object in self.myArray)
[self.concatenatedArray addObject:[NSString stringWithFormat:#"%#-%#",[object class], object.theProperty]];
self.mySet=[NSSet setWithArray:self.concatenatedArray];
I am not sure what you will use the NSSet output for but you can probably modify the concatenation elements to have the information you need in the NSSet output.
I have created a simple library, called Linq to ObjectiveC, which is a collection of methods that makes this kind of problem much easier to solve. In your case you need the Linq-to-ObjectiveC distinct method:
NSSet* dictionary = [NSSet setWithArray:[sourceArray distinct:^id(id item) {
return [item type] ;
}]];
This returns a set where each item has a distinct type property.
I have an array of strings, from which I would like to extract only those with unique character sets. (For example, "asdf" and "fdsa" would be considered redundant). This is the method I am currently using:
NSMutableArray *uniqueCharSets = [[NSMutableArray alloc] init];
NSMutableArray *uniqueStrings = [[NSMutableArray alloc] init];
for (NSString *_string in unique) {
NSCharacterSet *_charSet = [NSCharacterSet characterSetWithCharactersInString:_string];
if (![uniqueCharSets containsObject:_charSet]) {
[uniqueStrings addobject:_string];
[uniqueCharSets addObject:_charSet];
}
}
This seems to work, but it's very slow and resource-intensive. Can anyone think of a better way to do this?
Using an NSDictionary, map each string's lexicographically-sorted equivalent to an NSArray of input strings: (e.g. adfs => [afsd, asdf, ...])
Walk through the dictionary, printing out keys (or their values) which only have single-element array values
I just put together a quick example of how I would approach this, but it turns out that it is more, odd, than you first expect. For one, NSCharacterSet doesn't implement equality to check contents. It only uses the pointer value. Based on this your example will NOT work properly.
My approach is to use an NSSet to deal with the hashing of these for us.
#interface StringWrapper : NSObject
#property (nonatomic, copy) NSString *string;
#property (nonatomic, copy) NSData *charSetBitmap;
- (id)initWithString:(NSString*)aString;
#end
#implementation StringWrapper
#synthesize string, charSetBitmap;
- (id)initWithString:(NSString*)aString;
{
if ((self = [super init]))
{
self.string = aString;
}
return self;
}
- (void)setString:(NSString *)aString;
{
string = [aString copy];
self.charSetBitmap = [[NSCharacterSet characterSetWithCharactersInString:aString] bitmapRepresentation];
}
- (BOOL)isEqual:(id)object;
{
return [self.charSetBitmap isEqual:[object charSetBitmap]];
}
- (NSUInteger)hash;
{
return [self.charSetBitmap hash];
}
#end
int main (int argc, const char * argv[])
{
#autoreleasepool {
NSMutableSet *stringWrappers = [[NSMutableSet alloc] init];
NSArray *strings = [NSArray arrayWithObjects:#"abc",#"aaabcccc",#"awea",#"awer",#"abcde", #"ehra", #"QWEQ", #"werawe", nil];
for (NSString *str in strings)
[stringWrappers addObject:[[StringWrapper alloc] initWithString:str]];
NSArray *uniqueStrings = [stringWrappers valueForKey:#"string"];
NSLog(#"%#", uniqueStrings);
}
return 0;
}
The code is pretty straightforward. We create a container object to cache the results of the character set's bitmap representation. We use the bitmap representation because NSData implements isEqual: appropriately.
The only thing that come in my mind is not to use containsObject: since NSMutableArray is not ordered (in general), we can assume that containsObject simply iterates the array starting from the beginning until he finds the object. This means O(n) (n comparisons in the worst case).
A better solution may consists in keeping the array ordered and use a custom search method using a dichotomic approach. This way you'll have a O(log n) complexity.
Of course, you must take care of keeping your array ordered (much more efficient than add and reorder), so you should use insertObject:atIndex: method to insert the element properly.
I have an empty mutable array. Is it possible to insert object at index 2 for example, while there's nothing at index 0 and 1? I mean to increase capacity dynamically or something like that. .Regards.
NSMutableArray is not a sparse array; it does not allow empty slots that can be filled in later. initWithCapacity: just hints to the array that it will be filled to a certain amount; it isn't generally necessary in practice and, unless you know exactly how many items you are going to shove in the array, don't bother calling it (just use init).
A mutable array will quite efficiently grow in size as objects are added.
If you need a data structure that supports "holes", then either use something else or put a placeholder object in the slots that are supposed to be empty.
I.e. if you wanted an array with 10 slots, you might do:
NSMutableArray *a = [NSMutableArray array];
for(int i = 0; i<10; i++) [a addObject: [NSNull null]];
You can then check if the retrieved object isEqual: [NSNull null] to know if the slot is empty or not. And you can use replaceObjectAtIndex:withObject: to stick an object at a specific index.
Or you could use a different data structure; a dictionary with the indices as the keys would work, for example.
You can use a NSPointerArray for that.
NSPointerArray is a mutable collection
modeled after NSArray but it can also
hold NULL values, which can be
inserted or extracted (and which
contribute to the object’s count).
Moreover, unlike traditional arrays,
you can set the count of the array
directly.
NSPointerArray is available in OS X v10.5 and later and iOS 6.0 and later. If you target a lower OS version you can, for example:
Use a NSMutableDictionary, wrap you indices into NSNumbers and use these as keys.
Use a NSMutableArray and fill the "holes" with NSNull objects.
Write yourself a SparseArray class using an underlying NSMutableDictionary. Something like this (minimal code, barely tested, but it should give you the idea).
#interface SparseArray : NSObject {
#private
NSMutableDictionary* _dict;
int count;
}
-(SparseArray*)initWithCapacity:(NSUInteger)anInt;
-(id)objectAtIndex:(int)anIndex;
-(void)insertObject:(id)anObject atIndex:(int)anIndex;
- (void)removeObjectAtIndex:(int)anIndex;
-(int)count;
#implementation SparseArray
-(SparseArray*)initWithCapacity:(NSUInteger)anInt {
if ((self = [super init])) {
_dict = [[NSMutableDictionary dictionaryWithCapacity:anInt] retain];
count = 0;
}
return self;
}
-(id)objectAtIndex:(int)anIndex {
NSNumber* key = [NSNumber numberWithInt:anIndex];
id object = [_dict objectForKey:key];
return object;
}
-(void)insertObject:(id)anObject atIndex:(int)anIndex {
NSNumber* key = [NSNumber numberWithInt:anIndex];
[_dict setObject:anObject forKey:key];
count++;
}
- (void)removeObjectAtIndex:(int)anIndex {
NSNumber* key = [NSNumber numberWithInt:anIndex];
id object = [_dict objectForKey:key];
if (object) {
[_dict removeObjectForKey:key];
count--;
}
}
-(int)count {
return count;
}
-(void)dealloc {
[_dict release];
[super dealloc];
}
#end
I have an array with custom objects. Each array item has a field named "name". Now I want to remove duplicate entries based on this name value.
How should I go about achieving this?
I do not know of any standard way to to do this provided by the frameworks. So you will have to do it in code. Something like this should be doable:
NSArray* originalArray = ... // However you fetch it
NSMutableSet* existingNames = [NSMutableSet set];
NSMutableArray* filteredArray = [NSMutableArray array];
for (id object in originalArray) {
if (![existingNames containsObject:[object name]]) {
[existingNames addObject:[object name]];
[filteredArray addObject:object];
}
}
You might have to actually write this filtering method yourself:
#interface NSArray (CustomFiltering)
#end
#implementation NSArray (CustomFiltering)
- (NSArray *) filterObjectsByKey:(NSString *) key {
NSMutableSet *tempValues = [[NSMutableSet alloc] init];
NSMutableArray *ret = [NSMutableArray array];
for(id obj in self) {
if(! [tempValues containsObject:[obj valueForKey:key]]) {
[tempValues addObject:[obj valueForKey:key]];
[ret addObject:obj];
}
}
[tempValues release];
return ret;
}
#end
I know this is an old question but here is another possibility, depending on what you need.
Apple does provide a way to do this -- Key-Value Coding Collection Operators.
Object operators let you act on a collection. In this case, you want:
#distinctUnionOfObjects
The #distinctUnionOfObjects operator returns an array containing the distinct objects in the property specified by the key path to the right of the operator.
NSArray *distinctArray = [arrayWithDuplicates valueForKeyPath:#"#distinctUnionOfObjects.name"];
In your case, though, you want the whole object. So what you'd have to do is two-fold:
1) Use #distinctUnionOfArrays instead. E.g. If you had these custom objects coming from other collections, use #distinctUnionOfArray.myCollectionOfObjects
2) Implement isEqual: on those objects to return if their .name's are equal
I'm going to get flak for this...
You can convert your array into a dictionary. Not sure how efficient this is, depends on the implementation and comparison call, but it does use a hash map.
//Get unique entries
NSArray *myArray = #[#"Hello", #"World", #"Hello"];
NSDictionary *uniq = [NSDictionary dictionaryWithObjects:myArray forKeys:myArray];
NSLog(#"%#", uniq.allKeys);
*Note, this may change the order of your array.
If you'd like your custom NSObject subclasses to be considered equal when their names are equal you may implement isEqual: and hash. This will allow you to add of the objects to an NSSet/NSMutableSet (a set of distinct objects).
You may then easily create a sorted NSArray by using NSSet's sortedArrayUsingDescriptors:method.
MikeAsh wrote a pretty solid piece about implementing custom equality: Friday Q&A 2010-06-18: Implementing Equality and Hashing
If you are worried about the order
NSArray * newArray =
[[NSOrderedSet orderedSetWithArray:oldArray] array]; **// iOS 5.0 and later**
It is quite simple in one line
NSArray *duplicateList = ...
If you don't care about elements order then (unordered)
NSArray *withoutDUP1 = [[NSSet setWithArray:duplicateList] allObjects];
Keep the elements in order then (ordered)
NSArray *withoutDUP2 = [[NSOrderedSet orderedSetWithArray:duplicateList] array];
Implement isEqual to make your objects comparable:
#interface SomeObject (Equality)
#end
#implementation SomeObject (Equality)
- (BOOL)isEqual:(SomeObject*)other
{
return self.hash == other.hash;
}
- (NSUInteger)hash
{
return self.name;///your case
}
#end
How to use:
- (NSArray*)distinctObjectsFromArray:(NSArray*)array
{
return [array valueForKeyPath:#"#distinctUnionOfObjects.self"];
}