Splitting array into multiple arrays alphabetically iOS

Question

I have an array it looks like

NSArray *array=@[@"apple",@"animal",@"ant",@"beat",@"bean".....];

I need to split into multiple arrays alphabetically

I am adding the piece of code what I tried

  NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF BEGINSWITH 'a'"];
  NSArray *aElements = [arrLastName filterUsingPredicate:predicate];

NSPredicate works good but at second line am getting an error I dont need to solve this error . only thing is reformation the array into multiple arrays alphabatecilly

 Initializing 'NSArray *__strong' with an expression of incompatible type 'void'

Initializing 'NSArray *__strong' with an expression of incompatible type 'void' — Code cracker
– Code cracker, Commented Feb 24, 2015 at 11:01

Paulw11 · Accepted Answer · 2015-02-24 11:18:56Z

2

You have confused the NSMutableArray method filterUsingPredicate with the NSArray method filteredArrayUsingPredicate. The former modifies the receiver NSMutableArray and returns void. The latter leaves the original array unchanged and returns a new array.

So what you wanted is -

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF BEGINSWITH 'a'"];
NSArray *aElements = [arrLastName filteredArrayUsingPredicate:predicate];

However this approach would require you to iterate the array multiple times. I would use the following approach -

 NSMutableDictionary *alphaArrays=[NSMutableDictionary new];
 for (NSString *word in arrLastName) {
    NSString *firstletter=[word substringToIndex:1];
    NSMutableArray *wordArray=alphaArrays[firstletter];
    if (wordArray == nil) {
       wordArray=[NSMutableArray new];
       alphaArrays[firstletter]=wordArray;
    }
    [wordArray addObject:word];
 }

edited Feb 24, 2015 at 11:18

answered Feb 24, 2015 at 11:04

Paulw11

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6 Comments

Paulw11 Over a year ago

It may be more efficient, however to simply iterate the array once, adding the elements to 1 of 26 mutable arrays as you go

Code cracker Over a year ago

error solved but primary thing is i need to split into another array alphabetically

Paulw11 Over a year ago

Yes, using this technique you will need to create 26 predicates and each predicate will iterate the array.

Code cracker Over a year ago

yes but the array elements not fetching into new array , i am getting empty array

Code cracker Over a year ago

its adding all elements into array @paulw

|

Midhun MP · Accepted Answer · 2015-02-24 11:05:17Z

1

The issue is with filterUsingPredicate: it filters the NSMutableArray itself and it won't return anything (return type is void) .

You need to use filteredArrayUsingPredicate: (It returns a filtered NSArray)

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF BEGINSWITH 'a'"];
NSArray *aElements     = [arrLastName filteredArrayUsingPredicate:predicate];

Check the NSMutableArray Class reference, you can see the methods declared like:

- (void)filterUsingPredicate:(NSPredicate *)predicate

- (NSArray *)filteredArrayUsingPredicate:(NSPredicate *)predicate

answered Feb 24, 2015 at 11:05

Midhun MP

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2 Comments

Code cracker Over a year ago

thanks for the answer @midhun , your answer solved the error but still array elements not fetching into new array

Midhun MP Over a year ago

@Coolcracker: Check the predicate and also check the arrLastName contains any data. In your code you are populating array and using arrLastName.

sehaswaran · Accepted Answer · 2015-02-24 11:15:49Z

1

Using this library , it would be easy to solve LinqToObjectiveC https://github.com/ColinEberhardt/LinqToObjectiveC

This library has the following method groupBy https://github.com/ColinEberhardt/LinqToObjectiveC#groupBy

   NSArray* input = @[@"James", @"Jim", @"Bob"];

   NSDictionary* groupedByFirstLetter = [input linq_groupBy:^id(id name) {
           return [name substringToIndex:1];
    }];

 // the returned dictionary is as follows:
has two keys "J" and "B" and corresponding arrays as values
 // {
   //     J = ("James", "Jim"); - First Array 
   //     B = ("Bob"); - Second Array
 // }

answered Feb 24, 2015 at 11:15

sehaswaran

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