NSMutableArray add object with order

Question

I have a NSMUtableArray which has elements, for example:

a,b,c,e

And I want to add an object d to behind c and before e. In other words, I'd like to insert an object to a sorted array.(The object can be a custom object, too)

I'd like to know : besides using for to find the position, is there any other method to implement it? It is better to use the iOS api.

Thanks.

Answer 1

You can use -[NSArray indexOfObject:inSortedRange:options:usingComparator:] to ask an NSArray for the index where an object should be inserted given an array range that’s currently sorted.

For example, assuming the entire array is sorted::

NSMutableArray *array = …;
id newObject = …;
NSComparator comparator = …;

NSUInteger newIndex = [array indexOfObject:newObject
                             inSortedRange:(NSRange){0, [array count]}
                                   options:NSBinarySearchingInsertionIndex
                           usingComparator:comparator];

[array insertObject:newObject atIndex:newIndex];

Since this method uses binary search, it is more efficient than iterating over all elements in the array.

The comparator is a block object that receives two objects of type id and returns an NSComparisonResult value.

Answer 2

To inject element to known index (position) use

- (void)insertObject:(id)anObject atIndex:(NSUInteger)index

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSMutableArray_Class/Reference/Reference.html

And to find position of object previously placed into NSMutableArray use

- (int)indexOfObject:(id)anObject

NSMutableArray - Get Arrays Index Integer By Searching With A String

Section Finding Objects in an Array
http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSArray_Class/NSArray.html

Answer 3

I'd just add the new object at either end and sort the array again. If the array you're adding to is already sorted, the re-sort that moves one object is going to be about as quick as anything you'd implement yourself.

NSMutableArray *things; // populated 
id newObject;
...
[things addObject:newObject atIndex:0];
[things sortUsingSelector:@selector(compare:)];