Here is the code. I have tested with NSString, and it return -1. But for NSMutableArray is 0 instead.
NSMutableArray *items = [[NSMutableArray alloc] init];
for(int i=0;i<10;i++)
{
[items addObject:[Possession randomPossession]];
}
/*for(int i=0;i<[items count];i++)
{
NSLog(#"%#", [items objectAtIndex:i]);
}*/
//Using Fast Enumeration
/*for(items in items)
{
NSLog(#"%#", items);
}*/
NSLog(#"%d", [items retainCount]);
I made mistake by using array in iteration. The correct one should be like this.
//Using Fast Enumeration
for(Possession *item in items)
{
NSLog(#"%#", item);
}
And the retainCount is back to normal as expected 1.
A) You should never look at retainCount, even for debugging. It's an internal implementation detail that can provide confusing results.
B) This:
for(items in items)
is almost certainly not what you mean -- you're using the array object ("items") as the iterator too! Something like:
for(Possession *item in items)
would make more sense.
update:
You might want to look at some of the examples in Apple's documentation on fast enumeration. You really want to have a separate variable that acts as your loop iterator. What you're doing (for(items in items)) sets items to each object in the array in turn, and when you exit the loop, items will be nil!
Related
I am attempting to use this array cleaning method, and there seems to be an error. I can't spot it, I know the array goes in with 3116 items, comes out with 3116 (and I know for a fact there are three duplicates.
Please advice, thanks!
-(NSArray*) removeDuplicates:(NSArray*)inputArray{
NSMutableArray *arrayToClean = [NSMutableArray arrayWithArray:inputArray];
for (int i =0; i<[arrayToClean count]; i++) {
for (int j=(i+1); j < [arrayToClean count]; j++) {
if ([[arrayToClean objectAtIndex:i] isEqual:[arrayToClean
objectAtIndex:j]]) {
[arrayToClean removeObjectAtIndex:j];
j--;
}
}
}
NSArray *arrayToReturn = [NSArray arrayWithArray:arrayToClean];
return arrayToReturn;
}
NSSet will make this a lot easier:
-(NSArray *)removeDuplicates:(NSArray *)inputArray {
NSSet *unique = [NSSet setWithArray:inputArray];
return [unique allObjects];
}
Please note that a set has no guaranteed order. If you need the objects in the array to be in a specific order then you should sort the resulting array as needed.
It may also be appropriate to use an NSSet instead of the original array, then you don't need to worry about duplicates at all. But this depends on the other needs of your array.
Hey You can use another alternative for this.You can use the NSSet here for this task.
NSSet declares the programmatic interface for static sets of distinct objects
You can use sets as an alternative to arrays when the order of elements isn’t important and performance in testing whether an object is contained in the set is a consideration—while arrays are ordered, testing for membership is slower than with sets.
You Just need To call below method.
-(NSArray *)removeDuplicates:(NSArray *)inputArray {
NSSet *finalData = [NSSet setWithArray:inputArray];
return [finalData allObjects];
}
If really face any problem in above way of cleaning ducplicates then you can try another Alterantive.
-(NSArray *)removeDuplicates:(NSArray *)inputArray {
NSMutableArray *inputArray1=[NSMutableArray arrayWithArray:inputArray];
NSMutableArray *finalARray=[[NSMutableArray alloc]init];
for (id obj in inputArray1)
{
if (![finalARray containsObject:obj])
{
[finalARray addObject: obj];
}
NSLog(#"new array is %#",finalARray);
}
return finalARray;
}
I hope it may help you ...
Here is a helper function I had in a previous project to do the exact same thing
- (NSMutableArray *)removeDuplicates:(NSMutableArray *)sortedArray{
NSMutableSet* valuesAdded = [NSMutableSet set];
NSMutableArray* filteredArray = [[NSMutableArray alloc] init];
NSString* object;
/* Iterate over the array checking if the value is a member of the set. If its not add it
* to the set and to the returning array. If the value is already a member, skip over it.
*/
for (object in sortedArray){
if (![valuesAdded member:object]){
[valuesAdded addObject:object];
[filteredArray addObject:object];
}
}
return filteredArray;
}
The title pretty much says it all, but just to clarify: I have an NSMutableDictonary containing several NSMutableArrays. What I would like to do is find any value that is present in multiple arrays (there will not be any duplicates in a single array) and return that value. Can someone please help? Thanks in advance!
Edit: For clarity's sake I will specify some of my variables:
linesMutableDictionary contains a list of Line objects (which are a custom NSObject subclass of mine)
pointsArray is an array inside each Line object and contains the values I am trying to search through.
Basically I am trying to find out which lines share common points (the purpose of my app is geometry based)
- (NSValue*)checkForDupes:(NSMutableDictionary*)dict {
NSMutableArray *derp = [NSMutableArray array];
for (NSString *key in [dict allKeys]) {
Line *temp = (Line*)[dict objectForKey:key];
for (NSValue *val in [temp pointsArray]) {
if ([derp containsObject:val])
return val;
}
[derp addObjectsFromArray:[temp pointsArray]];
}
return nil;
}
this should work
If by duplicates you mean returning YES to isEqual: you could first make an NSSet of all the elements (NSSet cannot, by definition, have duplicates):
NSMutableSet* allElements = [[NSMutableSet alloc] init];
for (NSArray* array in [dictionary allValues]) {
[allElements addObjectsFromArray:array];
}
Now you loop through the elements and check if they are in multiple arrays
NSMutableSet* allDuplicateElements = [[NSMutableSet alloc] init];
for (NSObject* element in allElements) {
NSUInteger count = 0;
for (NSArray* array in [dictionary allValues]) {
if ([array containsObject:element]) count++;
if (count > 1) {
[allDuplicateElements addObject:element];
break;
}
}
}
Then you have your duplicate elements and don't forget to release allElements and allDuplicateElements.
When I do the following my application crashes and I get an error (terminate called after throwing an instance of 'NSException') whenever i run the simulation:
for (...)
[Array1 replaceObjectAtIndex:i withObject: [NSString stringWithFormat:#" Trip %i",i+1]]
OK after writing the problem I have found that the error is "0 is beyond bounds for empty array".
You really really really need to post the type of exception and your code to give us a reasonable chance of solving your problem. However, I'm going to taker a shot at it anyway.
My guess is your code looks something like this:
Array1 = [[NSMutableArray alloc] initWithCapacity: someNumber];
for (i = 0 ; i < someNumber ; ++i)
{
[Array1 replaceObjectAtIndex:i withObject: [NSString stringWithFormat:#" Trip %i",i+1]];
}
All arrays start out with 0 objects in them even if you use -initWithCapacity:. That method only provides a hint to the runtime that the array will grow to the specified size at some point. You need to use -addObject:.
Edit
Yep, from your edit, I'm sure I am right. The array has started out empty and you are trying to replace the object at index 0 which isn't there yet.
The code above should be changed as follows:
array1 = [[NSMutableArray alloc] initWithCapacity: someNumber]; // fixed naming convention too :-)
for (i = 0 ; i < someNumber ; ++i)
{
[array1 addObject: [NSString stringWithFormat:#" Trip %i",i+1]];
}
-addObject: adds the new objects to the end of the array.
If you want something that looks more like a C or Java array, you can prefill the array with NSNull objects
array1 = [[NSMutableArray alloc] initWithCapacity: 6]; // fixed naming convention too :-)
for (i = 0 ; i < 6 ; ++i)
{
[array1 addObject: [NSNull null]];
}
// Now the following will work
[array1 replaceObjectAtIndex: 4 withObject: #"foo"];
if you are using replaceObjectAtIndex method with NSArray array type object, there is possibility of getting exception (crashed).
Use NSMutableArray for managing a modifiable array of objects.
Although replaceObjectAtIndex can also be raised the following Exception for Object and Index
Index: Raises an NSRangeException if index is beyond the end of the array.
Object: Raises an NSInvalidArgumentException if Object you are passing is nil.
Ok, here is a guess (I can't do better without more information):
You cannot change an object you are iterating over.
(Bad) Example:
for (NSObject *obj in Array1){
[Array1 replaceObjectAtIndex:i withObject: [NSString stringWithFormat:#" Trip %i",i+1]]
}
I am trying to detect if an array isn't empty in order to be able to do a certain call.
I tried using if (![array ==nil]) however that doesn't compile.
I'm sure there is a really easy explanation to this.
Update
If array is empty I want to do this:
array = [[NSMutableArray alloc]init];
If it has an object I want to do this:
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
If you declared it but did not assign anything to it at all:
NSMutableArray *array;
Then the array will be nil, meaning it isn't there at all so you can't say if it's empty or not, so you can't check anything.
If you did assign something to it, and you want to find out if the existing array is empty or not, that would depend on how you created it first.
If the array was assigned from some convenience method, it's autoreleased, so just do this:
if ([array count] == 0) {
array = [[NSMutableArray alloc] init];
} else {
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
}
If the array was assigned from an init or copy method, or it was retained previously, store the count in a temporary variable, release the array and use the temporary variable to decide what to do:
NSInteger count = [array count];
[array release];
if (count == 0) {
array = [[NSMutableArray alloc] init];
} else {
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
}
In your case I'd always use without differentation
array = [[userDefaults arrayForKey:#"MyFavorites"] mutableCopy];
and set the default value in the user defaults to an empty array right away at program start before accessing the defaults (from Apple's example):
+ (void)initialize{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSDictionary *appDefaults = [NSDictionary
dictionaryWithObject:[NSArray array] forKey:#"MyFavorites"];
[defaults registerDefaults:appDefaults];
}
See Apple's doc on this.
Supposing you are talking about NSArray, if myArray has not been properly alloced+initialized (what you are trying to check) its reference will be nil, so you can do:
if(myArray) //or even if(myArray != nil) since myArray will be a pointer
{
//properly inizialized
}
else
{
//not properly inited
}
If it's been inited on the other hand, you can test its emptiness by checking the count property which returns the number of elements it contains
if([myArray > 0])
//there is at least one element
}
else
{
//no elements
}
you can use count function of NSArray. it will work on NSMutableArray too....
syntext will be,
int ct=[array count];
ct will have number of items in array.
if it us empty it will be Zero
I have an array, which contains some duplicate entries.
Firstly, is there any way to restrict duplicate entries when data getting inserted?
Secondly, if an array already having duplicate values than in some other way, we can retrieve only unique values from that array, I heard about NSSet about this, but I have no idea how to use it.
Don't use an NSSet.
You can only insert elements upon creation and cannot change the elements contained after you have created it.
If you want to add and remove objects on the fly, you can use an NSMutableSet.
Here is a demo of how to use it both NSSet and NSMutableSet, then converting the NSSet back to an NSArray (incase you want to do that):
- (void) NSMutableSetPrintTest
{
NSMutableSet *mutableSet = [[NSMutableSet alloc] init];
NSLog(#"Adding 5 objects (3 are duplicates) to NSMutableSet");
NSString *firstString = #"Hello World";
[mutableSet addObject:firstString];
[mutableSet addObject:#"Hello World"];
[mutableSet addObject:#"Goodbye World"];
[mutableSet addObject:#"Goodbye World"];
[mutableSet addObject:#"Goodbye World"];
NSLog(#"NSMutableSet now contains %d objects:", [mutableSet count]);
int j = 0;
for (NSString *string in mutableSet) {
NSLog(#"%d: %# <%p>", j, string, string);
j++;
}
NSLog(#"Now, if we are done adding and removing things (and only want to check what is in the Set) we should convert to an NSSet for increased performance.");
NSSet *immutableSet = [NSSet setWithSet:mutableSet];
NSLog(#"NSSet now contains %d objects:", [immutableSet count]);
int i = 0;
for (NSString *string in immutableSet) {
NSLog(#"%d: %# <%p>", i, string, string);
i++;
}
[mutableSet release]; mutableSet = nil;
NSLog(#"Now, if we are done with the sets, we can convert them back to an NSArray:");
NSArray *array = [immutableSet allObjects];
NSLog(#"NSArray contains %d objects", [array count]);
int k = 0;
for (NSString *string in array) {
NSLog(#"%d: %# <%p>", k, string, string);
k++;
}
}
NSMutableSet is probably the most logical thing to use.
However, be warned that a set does not maintain order of its elements (since a set, by definition, is unordered).
If that's a problem for you, then you have a couple of options:
duplicate set functionality with an NSMutableArray by invoking containsObject: before every call to addObject: (doable, but potentially slow, since arrays have O(n) search time)
use another object.
If you go with the second option, I would recommend taking a look at the excellent CHDataStructures framework, which has a subclass of NSMutableSet called CHOrderedSet, which is a set that maintains insertion order. (And since it's a subclass, it has the exact same API as an NSMutableSet)
If you've heard about NSSet, did you read the documentation? The API is similar to NSArray and very straightforward. Just like NSArray vs. NSMutableArray, you would use NSMutableSet if you need on the fly membership tests.