taking out objects from NSMutableArray

Question

I have an array which contains objects some may be same and some are different.
How can I take each same objects and different objects separately ?

Below is the array

NSMutableArray *items = [[NSMutableArray alloc]
 initWithArray:[NSArray arrayWithObjects:@"rat", @"rat", @"cat",@"Lion", @"cat", @"dog", @"dog", nil]];

I want to have four arrays which will contains these items :

First array with two rats
2nd array with two cats
3rd array with one lion
4th array with two dogs

What could be the best way to take the objects out ? Identical object should be placed in same array.

Abizern · Accepted Answer · 2011-12-29 15:10:45Z

6

Here's a general answer:

Put the array into an NSCountedSet - that will store each object and a count of the number of times it has been added.

Then - for each object in this counted set create an array with that object repeated according to the count of each object.

It will work in your case, because you are using static strings, which are going to be the same if they are the same string. This will take more work if you are using custom objects.

But the real question we have to ask is why you need to create these repetitive structures. If we could know what you are doing with it, we could give you better advice about how to go about it. For example, if you just need to keep a running count of the number of each type of object you have, you could just use the NSCountedSet directly (it descends from NSMutableSet, so it is already mutable) and not bother with creating the arrays.

edited Dec 29, 2011 at 15:10

answered Dec 29, 2011 at 15:05

Abizern

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3 Comments

ashish Over a year ago

I have a data base which contains multiple rows. Each row contains section title column. Some rows have same section title value and some have different. To load this data into table view I need data based on sections. Any good suggestion how can I retrieve that data. I am using core data.

Abizern Over a year ago

You're probably better off using an NSFetchedResultsController in that case.

ashish Over a year ago

Thank you Abizem. If I need to use NSCountedSet for custom objects in array. what would be the approach?

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