Filter array by first letter of string property

问题

I have an NSArray with objects that have a name property.

I would like filter the array by name

    NSString *alphabet = [agencyIndex objectAtIndex:indexPath.section];
    //---get all states beginning with the letter---
    NSPredicate *predicate =
    [NSPredicate predicateWithFormat:@"SELF beginswith[c] %@", alphabet];
    NSMutableArray *listSimpl = [[NSMutableArray alloc] init];
    for (int i=0; i<[[Database sharedDatabase].agents count]; i++) {
        Town *_town = [[Database sharedDatabase].agents objectAtIndex:i];
        [listSimpl addObject:_town];
    }
    NSArray *states = [listSimpl filteredArrayUsingPredicate:predicate];

But I get an error - "Can't do a substring operation with something that isn't a string (lhs = <1, Arrow> rhs = A)"

How can I do this? I would like to filter the array for the first letter in name being 'A'.

回答1:

Try with following code

NSPredicate *pred = [NSPredicate predicateWithFormat:@"SELF like %@", yourName];
NSArray *filteredArr = [yourArray filteredArrayUsingPredicate:pred];

EDITED :

NSPredicate pattern should be:

NSPredicate *pred =[NSPredicate predicateWithFormat:@"name beginswith[c] %@", alphabet];

回答2:

Here is one of the basic use of NSPredicate for filtering array .

NSMutableArray *array =
[NSMutableArray arrayWithObjects:@"Nick", @"Ben", @"Adam", @"Melissa", @"arbind", nil];

NSPredicate *sPredicate = [NSPredicate predicateWithFormat:@"SELF contains[c] 'b'"];
NSArray *beginWithB = [array filteredArrayUsingPredicate:sPredicate];
NSLog(@"beginwithB = %@",beginWithB);

回答3:

NSArray offers another selector for sorting arrays:

NSArray *sortedArray = [array sortedArrayUsingComparator:^NSComparisonResult(Person *first, Person *second) {
    return [first.name compare:second.name];
}];

回答4:

If you want to filter array take a look on this code:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"name == %@", @"qwe"];
NSArray *result = [self.categoryItems filteredArrayUsingPredicate:predicate];

But if you want to sort array take a look on the following functions:

- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context;
- (NSArray *)sortedArrayUsingFunction:(NSInteger (*)(id, id, void *))comparator context:(void *)context hint:(NSData *)hint;
- (NSArray *)sortedArrayUsingSelector:(SEL)comparator;

回答5:

visit https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Collections/Articles/Arrays.html

use this

[listArray sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];

回答6:

Checkout this library

https://github.com/BadChoice/Collection

It comes with lots of easy array functions to never write a loop again

So you can just do

NSArray* result = [thArray filter:^BOOL(NSString *text) {
    return [[name substr:0] isEqualToString:@"A"]; 
}] sort];

This gets only the texts that start with A sorted alphabetically

If you are doing it with objects:

NSArray* result = [thArray filter:^BOOL(AnObject *object) {
    return [[object.name substr:0] isEqualToString:@"A"]; 
}] sort:@"name"];

来源：https://stackoverflow.com/questions/18714634/filter-array-by-first-letter-of-string-property

标签

ios

objective-c

cocoa-touch

filter

nsarray