Numbers in NSMutableDictionary

Question

I am trying to setup a dictionary to have a string key with a numeric value (that needs to be incremented.

This is how I am initializing with value 1.

[person.list setObject:[NSNumber numberWithInteger:1] forKey:name];

How would I go about incrementing the value as needed?

From my understanding, an NSDictionary can only hold objects as the value, wouldn't this prevent me from just typing numbers? — john cs, Apr 30 '13 at 04:45

score 8 · Accepted Answer · answered Apr 30 '13 at 04:53

Get the object from the dictionary for the key, do the modification and then add that object to the dictionary for same key, this will replace previous object.

NSInteger number = [[dict objectForKey:name] integerValue];
number+=1;

[dict setObject:[NSNumber numberWithInteger:number] forKey:name];

score 1 · Answer 2 · edited May 23 '17 at 12:17

Use a sweet-ass category,

@interface NSNumber (NSNumber_Incrementing)    
-(NSNumber *)increment;    
@end

@implementation NSNumber (NSNumber_Incrementing)    
-(NSNumber *)increment {
     return [NSNumber numberWithInt:[self intValue] + 1];
}


[person.list setObject:[mynumb increment] forKey:name];

that means you need to hold mynumb

Add a protocol for NSDecimal et al.

@protocol Incrementing
- (NSNumber *)increment;
@end
so the above might be
@interface NSNumber (NSNumber_Incrementing) <Incrementing>
...
@interface NSDecimableNumber (NSNumber_Incrementing) <Incrementing>

But even f*ng sweeter is a category on Dictionary:

@interface NSDictionary (NSDictionary_SweetIncrementing) 
    -(void) incrementNumberForKey:name;  
@end

@implementation NSDictionary (NSDictionary_SweetIncrementing) 
-(void) incrementNumberForKey:name throws NSNumberException {
         NSNumber numb = (NSNumber *)[self valueForKey: name];         
         return [self setValue: [numb increment] forKey: name];
}
@end

valueForKey and setValue belong to NSDictionary. You are using a NSMutableDictionary that offers objectForKey and setObject.... so do that instead if so desired.

Yeah. And add some exceptions for key not associated with number

A similar question

`increment` makes it sound like the `NSNumber` itself is changing, which is impossible because it's not mutable. I'd change the method name to something else. — StilesCrisis, Apr 30 '13 at 05:27
Hi I'm trying to use the category on dictionary though I'm, getting this error. **Expected ':'** on the line -> throws NSNumberException. I ended up just deleting throws NSNumberException and it works great. Really nice way to make helpers in Objective C. Just curious but why place this in the category -> (NSDictionary_SweetIncrementing)? — uplearned.com, Jun 05 '20 at 06:42

score 0 · Answer 3 · edited May 23 '17 at 11:54

0

If its sequential increment than a static integer will be helpful!

static int increment = 1;

[person.list setObject:[NSNumber numberWithInteger:increment++] forKey:name];

If you're unaware of static variables, this question can be helpful.

edited May 23 '17 at 11:54

Community

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answered Apr 30 '13 at 04:45

Hemang

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I have many entries in the dictionary that could be in many different quantities. – john cs Apr 30 '13 at 04:49

score 0 · Answer 4 · answered Apr 30 '13 at 04:46

0

Not really sure what you are trying to achieve, but one solution could be

[person.list setObject:[NSNumber numberWithInteger:person.list.count+1] forKey:name];

answered Apr 30 '13 at 04:46

Erik

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I don't need to know the current numbers of entries in the dictionary, my goal is to retrieve the current integer that is the value and increment it by 1. – john cs Apr 30 '13 at 04:48
@johnhannigan And what prevents you from that, seriously? – Apr 30 '13 at 04:51
@johnhannigan **Are you serious?** I've been developing for iOS for 3 years. I know `NSDictionary` can hold Objective-C objects only, but this is so trivial I had a hard time understanding what your problem was at all. – Apr 30 '13 at 05:02

score 0 · Answer 5 · answered Apr 30 '13 at 04:56

0

    NSNumber *num = [person.list objectForKey:name];
    if(!num) [person.list setObject:[NSNumber numberWithInteger:1] forKey:name];
    else [person.list setObject:[NSNumber numberWithInteger:([num intValue]+1)] forKey:name];

answered Apr 30 '13 at 04:56

Thilina Chamath Hewagama

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score 0 · Answer 6 · answered Apr 30 '13 at 05:03

First, make sure person.list is an instance of NSMutableDictionary. (Also might want to change the list property on person to a different name. List implies an Array-like structure rather than a Dictionary.)

You can use the new NSDictionary syntax and the primitive to object boxing. I'm assuming the number is an unsigned integer here.

person.list[name] = @([person.list[name] unsignedIntegerValue] + 1);

That is syntactically similar to (split into multiple lines for readability)

NSUInteger previous = [[person.list objectForKey:name] unsignedIntegerValue];
NSNumber *incremented = [NSNumber numberWithUnsignedInteger:previous + 1];
[person.list setObject:incremented forKey:name];

The @(...) syntax converts a primitive number to an NSNumber object. While the [name] syntax is shorthand for setObject:forKey: of NSMutableDictionary.

Numbers in NSMutableDictionary

6 Answers6