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PONSArray find object or objects - best practices
 

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    <p><strong>Solution:</strong> I have marked @BlackRider's answer as correct as it is the most versatile especially for complex comparisons however there are other very good answers and comments. I would encourage anyone with the same or similar question to review them and evaluate the best course of action for your specific situation.</p> <p>In my situation, I am actually not using BlackRider's solution in my implementation. I have elected to use my own solution (see Edit #2 below) with help from @JoshCaswell's comments as well as @voromax's suggestion of <code>indexesOfObjectsWithOptions:passingTest:</code> due to the fact that my comparisons are very simple in this situation. </p> <p>Thanks to everyone who answered and provided insight.</p> <hr> <p>I am looking for an efficient way to retrieve an object from an <code>NSArray</code> based on a property of that object (a unique identifier, in this case). In C#.NET using Linq I would do something like</p> <pre><code>MyObject obj = myList.Single(o =&gt; o.uuid == myUUID); </code></pre> <p>I am also wondering if there is an efficient way to get an array of objects matching a non-unique property. Again, with Linq it would look like</p> <pre><code>List&lt;MyObject&gt; objs = myList.Where(o =&gt; o.flag == true).ToList(); </code></pre> <p>Of course I can write loops to do this but they would not be reusable and I'm suspicious of their performance.</p> <p>Finding an object with a unique ID:</p> <pre><code>-(MyObject*)findObjectWithUUID:(NSString*)searchUUID{ for (MyObject* obj in _myArray){ if([obj.uuid isEqualToString: searchUUID]) return obj; } } </code></pre> <p>Finding an array of objects:</p> <pre><code>-(NSArray*)findObjectsWithFlag:(BOOL)f{ NSMutableArray* arr = [NSMutableArray array]; for (MyObject* obj in _myArray){ if(obj.flag == f) [arr addObject:obj]; } return arr; } </code></pre> <p><strong>-- EDIT --</strong></p> <p>Luckily in the first situation the object I am looking for has a unique identifier and I know there will only be one. I came up with a solution to implement isEqual on my object which will be invoked by <code>indexOfObject:</code></p> <pre><code>- (BOOL)isEqual:(id)object{ return [self.uuid isEqualToString: ((MyObject*)object).uuid]; } </code></pre> <p>And then create a "fake" lookup object and use that to find the real one</p> <pre><code>MyObject *lookupObject = [[MyObject alloc] init]; lookupObject.uuid = searchUUID; MyObject *actualObject = [_myArray objectAtIndex:[_myArray indexOfObject:lookupObject]]; </code></pre> <p>This is essentially the same as the for-in loop I posted above, but might be more readable &amp; be more reusable. Of course, this only works for finding one unique object and does not address the second half of my question.</p> <p><strong>-- EDIT 2 --</strong></p> <p>Checking <code>Class</code> and implementing <code>hash</code> as recommended in comments.</p> <pre><code>- (BOOL)isEqual:(id)object{ return [object isKindOfClass:[MyObject class]] &amp;&amp; [self.uuid isEqualToString: ((MyObject*)object).uuid]; } - (NSUInteger)hash{ return [self.uuid hash]; } </code></pre>
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    1. COThe code you posted is about as efficient as it gets. Using things like predicates is going to be much slower than a purpose built loop.
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    2. COpossible duplicate of [Fast way to search the properties of objects in an NSArray](http://stackoverflow.com/questions/12099867/fast-way-to-search-the-properties-of-objects-in-an-nsarray)
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    3. COThank you @JoshCaswell. `[NSPredicate]` has been suggested below as well but @rmaddy mentioned performance concerns with it. I am curious how it compares to direct loops as well as `[indexesOfObjectsPassingTest:]`.I have edited my question with a possible solution for the first part of the question regarding a single object with a unique identifier. Are there any issues that may arise from this implementation?
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