NSPredicate on NSDictionary

Question

I'm trying to make sections in a table view based on the alphabet and sort my entries alphabetically under these sections.

I have collected the first letter in every entry of bandsArray in bandsArrayIndex and I'm now trying to use NSPredicate to count how many of each letter there are.

I'm doing this by following this guide.

They are using an NSArray and I'm using an NSDictionary and can't seem to get it to work. Can anyone help me out?

The application crashes when trying to show the view with the table view in it. In Debugger Console the following error is shown:

* Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Can't do a substring operation with something that isn't a string

This is my code

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSString *alphabet = [bandsArrayIndex objectAtIndex:section];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF beginswith[c] %@", alphabet];
    NSArray *letters = [bandsArray filteredArrayUsingPredicate:predicate];

    return [letters count];
}

EDIT: This is my bandsArray.

The header

NSMutableArray *bandsArray;

@property (nonatomic, retain) NSMutableArray* bandsArray;

The implementation

// set array from plist
NSString *path = [[NSBundle mainBundle] pathForResource:@"Bands" ofType:@"plist"];
NSMutableArray* tmpArray = [[NSMutableArray alloc] initWithContentsOfFile:path];

self.bandsArray = tmpArray;

// sort array after name ascending
NSSortDescriptor *nameSorter = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES selector:@selector(caseInsensitiveCompare:)];
[bandsArray sortUsingDescriptors:[NSArray arrayWithObject:nameSorter]];

You're leaking memory like a sieve when you create `bandsArray`. — Dave DeLong, Feb 04 '11 at 19:38
Can you show your bandsArray ? Is it just a NSString array ? I had no such problems with NSPredicate. It should be just a simple detail. If your bandsArray is not of NSStrings, you should filter by the property you're looking for. — Bruno Fuster, Feb 04 '11 at 19:02

score 22 · Accepted Answer · answered Feb 04 '11 at 18:59

22

Do you mean that bandsArray is an array of dictionaries? If so, and assuming each dictionary has a name key, you should be able to change the predicate to something like @"SELF.name beginswith[c] %@".

If, on the other hand, bandsArray is actually a dictionary itself, maybe you want to do [[bandsArray allKeys] filteredArrayUsingPredicate...].

answered Feb 04 '11 at 18:59

Daniel Dickison

21,832
13
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`@"SELF.name beginswith[c] %@"` did the trick! Thank you very much! – simonbs Feb 04 '11 at 19:47

score 6 · Answer 2 · answered Aug 01 '13 at 19:06

6

#import <Foundation/Foundation.h>
// clang -framework Foundation Siegfried.m 
    int
main() {
    NSArray *arr = @[
        @{@"1" : @"Fafner"},
        @{@"1" : @"Fasolt"}
    ];
    NSPredicate *p = [NSPredicate predicateWithFormat: @"SELF['1'] CONTAINS 'e'"];
    NSArray *res = [arr filteredArrayUsingPredicate:p];
    NSLog(@"Siegfried %@", res);
    return 0;
}

answered Aug 01 '13 at 19:06

Isaak Osipovich Dunayevsky

354
9
19

1

Thank @isaak it helped me a lot – Vaibhav Limbani Apr 20 '17 at 07:28

score 0 · Answer 3 · edited May 23 '17 at 10:31

Sorry, I didnt notice you had a NSArray of NSDictionaries.

Read this thread: Using NSPredicate to filter an NSArray based on NSDictionary keys

When you use NSDictionary, you should check by its Key... I'm not sure you're using the right approach!

I would do something like: @implementation Word : NSObect { NSString *title; }

then I would create a NSArray of Words and filter on them with: @"title beginswith[c] %@"

NSPredicate on NSDictionary

3 Answers3

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