NSArray:删除具有重复属性的对象

Question

我有一个包含一些自定义对象的NSMutableArray.其中两个对象具有相同的属性,如标题和作者.我想删除重复的对象,然后离开另一个.

Asset *asset;
NSMutableArray *items = [[[NSMutableArray alloc] init] autorelease];

// First
asset = [[Asset alloc] init];
asset.title = @"Developer";
asset.author = @"John Smith";
[items addObject:asset];
[asset release];

// Second
asset = [[Asset alloc] init];
asset.title = @"Writer";
asset.author = @"Steve Johnson";
[items addObject:asset];
[asset release];

// Third
asset = [[Asset alloc] init];
asset.title = @"Developer";
asset.author = @"John Smith";
[items addObject:asset];
[asset release];

由于它们不是同一个对象,但只有重复属性,我该如何删除副本？

Answer 1

您可以创建一个HashSet,并在循环时,可以将"title + author"连接集添加到HashSet(NSMutableSet).当您到达每个项目时,如果HashSet包含您的密钥,请将其删除或不复制(删除或创建没有重复项的副本).

这使它成为n阶(1循环)

这是NSMutableSet类:

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSMutableSet_Class/Reference/NSMutableSet.html#//apple_ref/occ/cl/NSMutableSet

编辑代码:

代码的核心是一个循环.

void print(NSMutableArray *assets)
{
    for (Asset *asset in assets)
    {
        NSLog(@"%@/%@", [asset title], [asset author]);
    }
}

int main (int argc, const char * argv[])
{

    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

    //
    // Create the initial data set
    //
    Asset *asset;
    NSMutableArray *items = [[[NSMutableArray alloc] init] autorelease];

    // First
    asset = [[Asset alloc] init];
    asset.title = @"Developer";
    asset.author = @"John Smith";
    [items addObject:asset];
    [asset release];

    // Second
    asset = [[Asset alloc] init];
    asset.title = @"Writer";
    asset.author = @"Steve Johnson";
    [items addObject:asset];
    [asset release];

    // Third
    asset = [[Asset alloc] init];
    asset.title = @"Developer";
    asset.author = @"John Smith";
    [items addObject:asset];
    [asset release];

    NSLog(@"****Original****");
    print(items);

    //
    // filter the data set in one pass
    //
    NSMutableSet *lookup = [[NSMutableSet alloc] init];
    for (int index = 0; index < [items count]; index++)
    {
        Asset *curr = [items objectAtIndex:index];
        NSString *identifier = [NSString stringWithFormat:@"%@/%@", [curr title], [curr author]];

        // this is very fast constant time lookup in a hash table
        if ([lookup containsObject:identifier])
        {
            NSLog(@"item already exists.  removing: %@ at index %d", identifier, index);
            [items removeObjectAtIndex:index];
        }
        else
        {
            NSLog(@"distinct item.  keeping %@ at index %d", identifier, index);
            [lookup addObject:identifier];
        }
    }

    NSLog(@"****Filtered****");
    print(items);

    [pool drain];
    return 0;
}

这是输出:

Craplet[11991:707] ****Original****
Craplet[11991:707] Developer/John Smith
Craplet[11991:707] Writer/Steve Johnson
Craplet[11991:707] Developer/John Smith
Craplet[11991:707] distinct item.  keeping Developer/John Smith at index 0
Craplet[11991:707] distinct item.  keeping Writer/Steve Johnson at index 1
Craplet[11991:707] item already exists.  removing: Developer/John Smith at index 2
Craplet[11991:707] ****Filtered****
Craplet[11991:707] Developer/John Smith
Craplet[11991:707] Writer/Steve Johnson