Convert NSArray to NSDictionary

Question

How can I convert an NSArray to an NSDictionary, using an int field of the array's objects as key for the NSDictionary?

Solution 1

- (NSDictionary *) indexKeyedDictionaryFromArray:(NSArray *)array 
{
  id objectInstance;
  NSUInteger indexKey = 0U;

  NSMutableDictionary *mutableDictionary = [[NSMutableDictionary alloc] init];
  for (objectInstance in array)
    [mutableDictionary setObject:objectInstance forKey:[NSNumber numberWithUnsignedInt:indexKey++]];

  return (NSDictionary *)[mutableDictionary autorelease];
}

Solution 2

Try this magic:

NSDictionary *dict = [NSDictionary dictionaryWithObjects:records 
                                   forKeys:[records valueForKey:@"intField"]];

FYI this is possible because of this built-in feature:

@interface NSArray(NSKeyValueCoding)

/* Return an array containing the results of invoking -valueForKey: 
on each of the receiver's elements. The returned array will contain
NSNull elements for each instance of -valueForKey: returning nil.
*/
- (id)valueForKey:(NSString *)key;

Solution 3

This adds a category extension to NSArray. Needs C99 mode (which is the default these days, but just in case).

In a .h file somewhere that can be #imported by all..

@interface NSArray (indexKeyedDictionaryExtension)
- (NSDictionary *)indexKeyedDictionary
@end

In a .m file..

@implementation NSArray (indexKeyedDictionaryExtension)

- (NSDictionary *)indexKeyedDictionary
{
  NSUInteger arrayCount = [self count];
  id arrayObjects[arrayCount], objectKeys[arrayCount];

  [self getObjects:arrayObjects range:NSMakeRange(0UL, arrayCount)];
  for(NSUInteger index = 0UL; index < arrayCount; index++) { objectKeys[index] = [NSNumber numberWithUnsignedInteger:index]; }

  return([NSDictionary dictionaryWithObjects:arrayObjects forKeys:objectKeys count:arrayCount]);
}

@end

Example use:

NSArray *array = [NSArray arrayWithObjects:@"zero", @"one", @"two", NULL];
NSDictionary *dictionary = [array indexKeyedDictionary];

NSLog(@"dictionary: %@", dictionary);

Outputs:

2009-09-12 08:41:53.128 test[66757:903] dictionary: {
    0 = zero;
    1 = one;
    2 = two;
}

Solution 4

- (NSDictionary *) indexKeyedDictionaryFromArray:(NSArray *)array
{
    NSMutableDictionary *mutableDictionary = [[NSMutableDictionary alloc] init];
    [array enumerateObjectsUsingBlock:
     ^(id obj, NSUInteger idx, BOOL *stop){
         NSNumber *index = [NSNumber numberWithInteger:idx];
         [mutableDictionary setObject:obj forKey:index];
     }];
    NSDictionary *result = [NSDictionary.alloc initWithDictionary:mutableDictionary];
    return result;
}

Solution 5

This is an example of creating a NSMutableDictionary from the employee list NSMutableArray:

 NSMutableArray *emloyees = [[NSMutableArray alloc]initWithObjects:@"saman",@"Ruchira",@"Rukshan",@"ishan",@"Harsha",@"Ghihan",@"Lakmali",@"Dasuni", nil];

 NSMutableDictionary *dict = [NSMutableDictionary dictionary];
 for (NSString *word in emloyees) {
 NSString *firstLetter = [[word substringToIndex:1] uppercaseString];
 letterList  = [dict objectForKey:firstLetter];

if (!letterList) {
    letterList = [NSMutableArray array];
    [dict setObject:letterList forKey:firstLetter];
}
[letterList addObject:word];}  NSLog(@"dic %@",dict);

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Comments

[Woofy]

I love using categories, so I'd preffer this solution instead of using a simple function because of the way of calling it directly on the object itself, as if it always knew that method.

[BootMaker]

It's really a magic! Elegant and really handy solution! Just a note: Maybe better to use [records valueForKey:@"otherField"] not just records, as it will contains "intField" too. Anyway it's new for me even after years of coding...