NSMutableArray check if object already exists

Question

I am not sure how to go about this. I have an NSMutableArray (addList) which holds all the items to be added to my datasource NSMutableArray.

I now want to check if the object to be added from the addList array already exists in the datasource array. If it does not exist add the item, if exists ignore.

Both the objects have a string variable called iName which i want to compare.

Here is my code snippet

-(void)doneClicked{
    for (Item *item in addList){
        /*
        Here i want to loop through the datasource array 
        */
        for(Item *existingItem in appDelegate.list){
            if([existingItem.iName isEqualToString:item.iName]){
                // Do not add
            }
            else{
                [appDelegate insertItem:item];
            } 
        }
}

But i find the item to be added even if it exists.

What am i doing wrong ?

It is a logic mistake, see my answer

knuku
– knuku

2011-06-09 11:04:02 +00:00
Commented Jun 9, 2011 at 11:04 — knuku
– knuku, Commented Jun 9, 2011 at 11:04

Bista · Accepted Answer · 2015-03-18 08:01:02Z

76

There is a very useful method for this in NSArray i.e. containsObject.

NSArray *array;
array = [NSArray arrayWithObjects: @"Nicola", @"Margherita",                                       @"Luciano", @"Silvia", nil];
if ([array containsObject: @"Nicola"]) // YES
{
    // Do something
}

edited Mar 18, 2015 at 8:01

Bista

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answered Sep 17, 2012 at 7:34

Black Tiger

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Comments

Neelesh · Accepted Answer · 2011-06-09 20:48:17Z

40

I found a solution, may not be the most efficient of all, but atleast works

NSMutableArray *add=[[NSMutableArray alloc]init];

for (Item *item in addList){
        if ([appDelegate.list containsObject:item])
            {}
        else
            [add addObject:item];
}

Then I iterate over the add array and insert items.

answered Jun 9, 2011 at 20:48

Neelesh

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Comments

EmptyStack · Accepted Answer · 2011-06-09 11:50:41Z

22

Use NSPredicate.

NSArray *list = [[appDelegate.list copy] autorelease];

for (Item *item in addList) {

    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"iName MATCHES %@", item.iName];
    NSArray *filteredArray = [list filteredArrayUsingPredicate:predicate];
    if ([filteredArray count] > 0) [appDelegate insertItem:item];
}

edited Jun 9, 2011 at 11:50

answered Jun 9, 2011 at 11:17

EmptyStack

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11 Comments

JeremyP Over a year ago

+1 nice answer. Also avoids the mutating collection exception that would happen if the method used in the question actually worked.

Neelesh Over a year ago

I tried the above edited solution. First thing, the program crashes without showing any error. Secondly, the Item is added even if it exists in the datasource list

Neelesh Over a year ago

@simon: thanks for the answer. But still the program crashes :( I am just banging my head now :(

EmptyStack Over a year ago

@Narayanan, Can you tell in which line the program crashes?

Neelesh Over a year ago

@simon: It crashes where we create the predicate. [NSComparisonPredicate isEqualToString:]: unrecognized selector sent to instance 0x7154070

|

knuku · Accepted Answer · 2011-06-09 11:26:26Z

6

Did you try indexOfObject:?

-(void)doneClicked{
    for (Item *item in addList){
        if([appDelegate.list indexOfObject:item] == NSNotFound){
            [appDelegate insertItem:item];
        }
}

UPDATE: You have a logical mistake, not mistake in code. assume the first array is ['a', 'b', 'c'], and the second is ['a', 'x', 'y', 'z']. When you iterate with 'a' through the second array it won't add 'a' to second array in the first iteration (compare 'a' with 'a') but will add during the second (compare 'a' with 'x'). That is why you should implement isEqual: method (see below) in your 'Item' object and use the code above.

- (BOOL)isEqual:(id)anObject {
    if ([anObject isKindOfClass:[Item class]])
        return ([self.iName isEqualToString:((Item *)anObject).iName]);
    else
        return NO;
}

edited Jun 9, 2011 at 11:26

answered Jun 9, 2011 at 10:36

knuku

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8 Comments

Neelesh Over a year ago

@NR4TR: i want to compare the names alone. Not the entire object

Neelesh Over a year ago

Yes i get it now. But when i use the code you have updated, I get the following error [Item isEqualToString:]: unrecognized selector sent to instance 0x712ee70

knuku Over a year ago

Check your isEqual: method implementation inside your Item class

Neelesh Over a year ago

sorry, I do not seem to follow. Item is a class that i created myself and I do not have an isEqual method at all. Can you please help me in detail ?

knuku Over a year ago

see updates. just paste this isEqual: method to your Item implementation

|

Charged Neuron · Accepted Answer · 2012-05-26 23:41:47Z

4

Have a look at NSSet. You can add objects and the object will only be added if the object is unique. You can create a NSSet from an NSArray or vise versa.

answered May 26, 2012 at 23:41

Charged Neuron

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Comments

Simon Lee · Accepted Answer · 2011-06-09 10:38:30Z

2

You can override isEquals and hash on the object so that it returns a YES / NO based on the comparison of the iName property.

Once you have that you can use...

- (void)removeObjectsInArray:(NSArray *)otherArray

To clean the list before adding all the remaining objects.

answered Jun 9, 2011 at 10:38

Simon Lee

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3 Comments

Neelesh Over a year ago

First, I want to compare the names alone and not the entire object.

knuku Over a year ago

Consider reading documentation about isEquals method, it could help

Simon Lee Over a year ago

Yes, the idea of overriding the isEquals is that you can then define what you consider 'equal'. Normally the runtime will look at two objects and if they are not the same instance will return false. By overriding the isEquals method you can say 'actually I don't care if the OBJECTS are not the same, in my eyes, these two items are the same if the name matches.'

saurabh · Accepted Answer · 2011-06-09 11:42:04Z

2

NR4TR said correctly but i think one break statement is sufficient


if([existingItem.iName isEqualToString:item.iName]){
                // Do not add
break;
            }

answered Jun 9, 2011 at 11:42

saurabh

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Comments

EmptyStack · Accepted Answer · 2011-06-09 12:53:54Z

1

Convert Lowercase and Trim whitespace and then check..

[string lowercaseString];

and

NSString *trim = [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

edited Jun 9, 2011 at 12:53

EmptyStack

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answered Jun 9, 2011 at 11:03

Rams

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Comments

Terence · Accepted Answer · 2015-04-13 02:56:30Z

1

You compare the addList's first object and appDelegate.list's first object, if they are not equal, you insert the addList's object. The logic is wrong, you should compare one addList's object with every appDelegate.list's object.

answered Apr 13, 2015 at 2:56

Terence

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