using wild card for the key in dictionary in C#

Question

I have a movie cache dictionary where key is string and value is movie.

Dictionary<string, Movie> movieCache = new Dictionary<string, Movie>();

movieCache.Add(string.Format("{0}:{1}:{2}", newMovie.Year, newMovie.Title, newMovie.Genre), newMovie);

I have another list say joe's favorite movie list. for example

List<IMDBMovie> joesFavMovie // some list;

I need to display two lists. One: the movies from the cache that is in joesFavMovie and matches the year, title and Genre. Two: the movies from the cache that is in joesFavMovie and matches the year, title.

I was able to display the first list form the cache. However i was creating another dictionary cache from the existing dictionary to display the second list. Is there a way to use the same cache for both the lists. I am not sure if wild card is the best solution.

Thanks in advance. The title might not be appropriate. please suggest if that needs to be changed.

Could you please clarify where do you use wildcard? The title is a bit misleading. Thanks and regards, — Alexander Bell, Dec 23 '14 at 13:49
@AlexBell, Thanks. I would like to use the wild card for key. Updated the title. — IamaC, Dec 23 '14 at 13:56
See this [answer](http://stackoverflow.com/a/9672624/945456). There is no wildcard search of dictionary keys without losing the O(1) lookup it provides. If performance really is critical (have you measured this and found it to be a bottleneck in your program that's causing problems?) then you may have to chose a different data-structure. — Jeff B, Dec 23 '14 at 14:10
@JeffBridgman I just created this example so that I can explain. It is not the actual scenario. However the problem is the same. Could you please suggest the architecture I should use? — IamaC, Dec 23 '14 at 14:29

score 1 · Answer 1 · answered Dec 23 '14 at 13:52

1

You can use LINQ for this.

List<Movie> movies = 
     movieCache.Where(m => m.Value.Year == 1975 && m.Value.Title == "Jaws")
               .ToList();

answered Dec 23 '14 at 13:52

Anthony Faull

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The lambda expression could easily use a Regex expression to do the matching, providing you a mechanism for using wildcards. – Tony Vitabile Dec 23 '14 at 13:57
@Anthony Faull. thanks for your answer. I am looking for more efficient solution where i get to use the cache as dictionary. something O(n) – IamaC Dec 23 '14 at 13:58
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@lamaC I'm pretty sure this answer is O(n); it only has to iterate once over the *n* items in the dictionary, checking which ones match along the way. Dictionary look-up using the key (e.g. `movieCache["1975:Jaws:Thriller"]`) is O(1). – Jeff B Dec 23 '14 at 14:07
@JeffBridgman, Please let me know if I am wrong here. If i run a foreach on joesFavMovie and then do a where on the cache that is O(n*n) right? if you are talking about the first list in my question then its O(n). I am trying to achieve same for the second. – IamaC Dec 23 '14 at 14:19
If they're nested then yes. You didn't have any code for that part in your question, so that escaped my notice. If the loops aren't nested, then it's just two O(n) (`2n` vs `n*n`). – Jeff B Dec 23 '14 at 14:35

score 0 · Answer 2 · edited Dec 23 '14 at 14:58

0

var list2 = movieCache.Where(
    m => joesFavMovie.Any(fm => fm.Year == m.Value.Year && 
                                fm.Title == m.Value.Title)).ToList();

edited Dec 23 '14 at 14:58

Jeff B

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answered Dec 23 '14 at 13:56

Kelvin Lai

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using wild card for the key in dictionary in C#

2 Answers2