Sort and Take N from dictionary value in C#

Question

I have a dictionary in C#.

Dictionary originalMap = new Dictionary<string, List<CustomObject>>();

originalMap contents: 
"abc" -> {CustomObject1, CustomeObject2, ..CustomObject100};
"def" -> {CustomObject101,CustomObject102, CustomObject103};

Now, finally I want to make sure that the count of all custome objects above does not exceed a limit - say 200. While doing this, I want to make sure that I take top 200 ranked object (sorted by Score porperty).

I tried below but it doesn't work. It returns same number of objects.

var modifiedMap = new Dictionary<string, IList<CustomObject>>(CustomObject);

modifiedMap = originalMap.OrderByDescending(map => map.Value.OrderByDescending(customObject => customObject.Score).ToList().Take(200))
                 .ToDictionary(pair => pair.Key, pair => pair.Value);

Any help will be appreciated. Thank you.

Are you trying to limit the total number in the dictionary to 200 or the total number per key to 200? — itsme86, Aug 11 '20 at 17:02
(My answer assumes a limit per key - if that's not what you want, please clarify your question.) — Jon Skeet, Aug 11 '20 at 17:36

score 4 · Accepted Answer · answered Aug 11 '20 at 17:01

You're only performing the limit part while doing the ordering - not when you actually create the new dictionary.

It sounds like you want something like:

var modifiedMap = originalMap.ToDictionary(
    pair => pair.Key,
    pair => pair.Value.OrderByDescending(co => co.Score).Take(200).ToList());

Note that ordering the dictionary entries themselves would be pointless, as Dictionary<TKey, TValue> is inherently not an ordered collection.

Sort and Take N from dictionary value in C#

1 Answers1