Tejas Shirodkar

I couldn’t find any pre existing way of getting the last index of an item in NSArray, so I ended up creating my own implementation.

Categories are a very cool feature of objective C and allow you to add functionality to pre-existing classes in a modular way.

After including the category as part of the build, a developer can simply import the category header and use lastIndexOf as it was part of NSArray or NSMutableArray.

[NSArray lastIndexOf:(id)anObject];

[NSMutableArray lastIndexOf:(id)anObject fromIndex:(NSUInteger)fromIndex];

Just add the following two files to your project and you are all set.

NSArray+LastIndexOf.h

//
//  NSArray+LastIndexOf.h
//
//  Created by Tejas Shirodkar on 9/6/13.
//  Copyright (c) 2013 Tejas Shirodkar, tejas@tejasshirodkar.com. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person
//  obtaining a copy of this software and associated documentation
//  files (the "Software"), to deal in the Software without
//  restriction, including without limitation the rights to use,
//  copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the
//  Software is furnished to do so, subject to the following
//  conditions:
//
//  The above copyright notice and this permission notice shall be
//  included in all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
//  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
//  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
//  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
//  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
//  OTHER DEALINGS IN THE SOFTWARE.

#ifndef NSArray_LastIndexOf_h
#define NSArray_LastIndexOf_h

@interface NSArray (LastIndexOf)
- (NSUInteger)lastIndexOf:(id)anObject;
- (NSUInteger)lastIndexOf:(id)anObject fromIndex:(NSUInteger)fromIndex;
@end

#endif

and NSArray+LastIndexOf.m

//
//  NSArray+LastIndexOf.m
//
//  Created by Tejas Shirodkar on 9/6/13.
//  Copyright (c) 2013 Tejas Shirodkar, tejas@tejasshirodkar.com. All rights reserved.
//
//  Permission is hereby granted, free of charge, to any person
//  obtaining a copy of this software and associated documentation
//  files (the "Software"), to deal in the Software without
//  restriction, including without limitation the rights to use,
//  copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the
//  Software is furnished to do so, subject to the following
//  conditions:
//
//  The above copyright notice and this permission notice shall be
//  included in all copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
//  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
//  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
//  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
//  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
//  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
//  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
//  OTHER DEALINGS IN THE SOFTWARE.

#include "NSArray+LastIndexOf.h"

@implementation NSArray (LastIndexOf)

- (NSUInteger)lastIndexOf:(id)anObject
{
    __block NSUInteger lastIndex = NSNotFound;
    [self enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id obj, NSUInteger idx, BOOL *stop)
     {
         if([obj isEqual:anObject])
         {
             *stop = YES;
             lastIndex = idx;
             return;
         }
     }];
    return lastIndex;
}

- (NSUInteger)lastIndexOf:(id)anObject fromIndex:(NSUInteger)fromIndex
{
    __block NSUInteger lastIndex = NSNotFound;
    [self enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id obj, NSUInteger idx, BOOL *stop)
     {
         if(idx < fromIndex)
             return;
         if([obj isEqual:anObject])
         {
             *stop = YES;
             lastIndex = idx;
             return;
         }
     }];
    return lastIndex;
}

@end

Happy Coding!