如何交换`NSMutableDictionary`键和值？

Question

我有一个NSMutableDictionary,我想交换值和键.即,交换后的值变为键,其对应的键变为值所有键和值都是唯一的.寻找一个适当的解决方案,因为尺寸非常大.此外,键和值是NSString对象

Answer 1

NSMutableDictionary *d = [NSMutableDictionary dictionaryWithDictionary:@{
                             @"key1" : @"value1",
                             @"key2" : @"value2"}];

for (NSString *key in [d allKeys]) {
    d[d[key]] = key;
    [d removeObjectForKey:key];
}

NSLog(@"%@", d); // => { value1 : key1,
                 //      value2 : key2 }

假设

• 唯一值(因为它们将成为键)
• 值符合NSCopying(与上述相同)
• 没有值等于任何键(否则在此过程中会丢失冲突的名称)

Answer 2

这是另一种反转字典的方法.对我来说最简单.

NSArray *keys = dictionary.allKeys;
NSArray *values = [dictionary objectsForKeys:keys notFoundMarker:[NSNull null]];
[dictionary removeAllObjects]; // In case of huge data sets release the contents.
NSDictionary *invertedDictionary = [NSDictionary dictionaryWithObjects:keys forKeys:values];
[dictionary setDictionary:invertedDictionary]; // In case you want to use the original dictionary.