The best way to remove duplicate values from NSMutableArray in Objective-C

Question

The best way to remove duplicate values  NSString  from NSMutableArray in Objective-C   Is this the easiest and right way to do it   uniquearray     NSSet setWithArray yourarray  allObjects

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need order   NSArray  yourarray       a    b    c    NSOrderedSet  orderedSet    NSOrderedSet orderedSetWithArray yourarray   NSArray  arrayWithoutDuplicates    orderedSet array   NSLog       arrayWithoutDuplicates     or don t need order  NSSet  set    NSSet setWithArray yourarray   NSArray  arrayWithoutOrder    set allObjects   NSLog       arrayWithoutOrder

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Remove duplicate values from NSMutableArray in Objective-C  NSMutableArray  datelistArray     NSMutableArray alloc init   for  Student   data in fetchStudentDateArray        if  datelistArray indexOfObject data date     NSNotFound       datelistArray addObject data date

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I know this is an old question  but there is a more elegant way to remove duplicates in a NSArray if you don t care about the order   If we use Object Operators from Key Value Coding we can do this   uniquearray    yourarray valueForKeyPath    distinctUnionOfObjects self      As AnthoPak also noted it is possible to remove duplicates based on a property  An example would be   distinctUnionOfObjects name

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Note that if you have a sorted array  you don t need to check against every other item in the array  just the last item   This should be much faster than checking against all items      sortedSourceArray is the source array  already sorted NSMutableArray  newArray     NSMutableArray alloc  initWithObjects  sortedSourceArray objectAtIndex 0    for  int i   1  i  lt   sortedSourceArray count   i          if     sortedSourceArray objectAtIndex i  isEqualToString  sortedSourceArray objectAtIndex  i-1                    newArray addObject  tempArray objectAtIndex i              It looks like the NSOrderedSet answers that are also suggested require a lot less code  but if you can t use an NSOrderedSet for some reason  and you have a sorted array  I believe my solution would be the fastest   I m not sure how it compares with the speed of the NSOrderedSet solutions   Also note that my code is checking with isEqualToString   so the same series of letters will not appear more than once in newArray   I m not sure if the NSOrderedSet solutions will remove duplicates based on value or based on memory location   My example assumes sortedSourceArray contains just NSStrings  just NSMutableStrings  or a mix of the two   If sortedSourceArray instead contains just NSNumbers or just NSDates  you can replace   if     sortedSourceArray objectAtIndex i  isEqualToString  sortedSourceArray objectAtIndex  i-1       with   if    sortedSourceArray objectAtIndex i  compare  sortedSourceArray objectAtIndex  i-1       NSOrderedSame    and it should work perfectly   If sortedSourceArray contains a mix of NSStrings  NSNumbers  and or NSDates  it will probably crash

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Here i removed duplicate name values from mainArray and store result in NSMutableArray listOfUsers   for  int i 0  i lt mainArray count  i          if  listOfUsers count  0             listOfUsers addObject  mainArray objectAtIndex i              else if    listOfUsers valueForKey   name    containsObject   mainArray objectAtIndex i  valueForKey   name                    NSLog   Same object              else                listOfUsers addObject  mainArray objectAtIndex i

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Yes  using NSSet is a sensible approach   To add to Jim Puls  answer  here s an alternative approach to stripping duplicates while retaining order      Initialise a new  empty mutable array  NSMutableArray  unique    NSMutableArray array    for  id obj in originalArray        if    unique containsObject obj              unique addObject obj             It s essentially the same approach as Jim s but copies unique items to a fresh mutable array rather than deleting duplicates from the original  This makes it slightly more memory efficient in the case of a large array with lots of duplicates  no need to make a copy of the entire array   and is in my opinion a little more readable   Note that in either case  checking to see if an item is already included in the target array  using containsObject  in my example  or indexOfObject inRange  in Jim s  doesn t scale well for large arrays  Those checks run in O N  time  meaning that if you double the size of the original array then each check will take twice as long to run  Since you re doing the check for each object in the array  you ll also be running more of those more expensive checks  The overall algorithm  both mine and Jim s  runs in O N2  time  which gets expensive quickly as the original array grows   To get that down to O N  time you could use a NSMutableSet to store a record of items already added to the new array  since NSSet lookups are O 1  rather than O N   In other words  checking to see whether an element is a member of an NSSet takes the same time regardless of how many elements are in the set   Code using this approach would look something like this   NSMutableArray  unique    NSMutableArray array   NSMutableSet  seen    NSMutableSet set    for  id obj in originalArray        if    seen containsObject obj              unique addObject obj            seen addObject obj             This still seems a little wasteful though  we re still generating a new array when the question made clear that the original array is mutable  so we should be able to de-dupe it in place and save some memory  Something like this   NSMutableSet  seen    NSMutableSet set   NSUInteger i   0   while  i  lt   originalArray count         id obj    originalArray objectAtIndex i        if   seen containsObject obj              originalArray removeObjectAtIndex i              NB  we  don t  increment i here  since            we ve removed the object previously at            index i   originalArray objectAtIndex i             now points to the next object in the array        else            seen addObject obj           i                UPDATE  Yuri Niyazov pointed out that my last answer actually runs in O N2  because removeObjectAtIndex  probably runs in O N  time     He says  probably  because we don t know for sure how it s implemented  but one possible implementation is that after deleting the object at index X the method then loops through every element from index X 1 to the last object in the array  moving them to the previous index  If that s the case then that is indeed O N  performance    So  what to do  It depends on the situation  If you ve got a large array and you re only expecting a small number of duplicates then the in-place de-duplication will work just fine and save you having to build up a duplicate array  If you ve got an array where you re expecting lots of duplicates then building up a separate  de-duped array is probably the best approach  The take-away here is that big-O notation only describes the characteristics of an algorithm  it won t tell you definitively which is best for any given circumstance

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There s a KVC Object Operator that offers a more elegant solution uniquearray    yourarray valueForKeyPath    distinctUnionOfObjects self    Here s an NSArray category

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Your NSSet approach is the best if you re not worried about the order of the objects  but then again  if you re not worried about the order  then why aren t you storing them in an NSSet to begin with   I wrote the answer below in 2009  in 2011  Apple added NSOrderedSet to iOS 5 and Mac OS X 10 7  What had been an algorithm is now two lines of code   NSOrderedSet  orderedSet    NSOrderedSet orderedSetWithArray yourArray   NSArray  arrayWithoutDuplicates    orderedSet array       If you are worried about the order and you re running on iOS 4 or earlier  loop over a copy of the array   NSArray  copy    mutableArray copy   NSInteger index    copy count  - 1  for  id object in  copy reverseObjectEnumerator         if   mutableArray indexOfObject object inRange NSMakeRange 0  index      NSNotFound             mutableArray removeObjectAtIndex index             index--     copy release

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If you are targeting iOS 5   what covers the whole iOS world   best use NSOrderedSet  It removes duplicates and retains the order of your NSArray   Just do  NSOrderedSet  orderedSet    NSOrderedSet orderedSetWithArray yourArray     You can now convert it back to a unique NSArray  NSArray  uniqueArray   orderedSet array    Or just use the orderedSet because it has the same methods like an NSArray like objectAtIndex   firstObject and so on   A membership check with contains is even faster on the NSOrderedSet than it would be on an NSArray  For more checkout the NSOrderedSet Reference

User · Answer

just use this simple code    NSArray  hasDuplicates                NSArray  noDuplicates     NSSet setWithArray  hasDuplicates  allObjects     since nsset doesn t allow duplicate values and all objects returns an array

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Available in OS X v10 7 and later   If you are worried about the order right way to do   NSArray  no     NSOrderedSet orderedSetWithArray originalArray allObjects     Here is the code of removing duplicates values from NSArray in Order

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One more simple way you can try out which will not add duplicate Value before adding object in array -    Assume mutableArray is allocated and initialize and contains some value  if    yourMutableArray containsObject someValue         yourMutableArray addObject someValue

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Here is the code of removing duplicates values from NSMutable Array  it will work for you  myArray is your Mutable Array that you want to remove duplicates values    for int j   0  j  lt   myMutableArray count   j         for  k   j 1 k  lt   myMutableArray count  k         NSString  str1    myMutableArray objectAtIndex j       NSString  str2    myMutableArray objectAtIndex k       if  str1 isEqualToString str2            myMutableArray removeObjectAtIndex k               Now print your array and will see there is no repeated value

User · Answer

Using Orderedset will do the trick  This will keep the remove duplicates from the array and maintain order which sets normally doesn t do

[ios] The best way to remove duplicate values from NSMutableArray in Objective-C?

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