c# - Why doesn't IGrouping inherit IEnumerable<KeyValuePair> like IDictionary? -

igrouping:

public interface igrouping<out tkey, out telement> : ienumerable<telement>,  ienumerable 

idictionary:

public interface idictionary<tkey, tvalue> : icollection<keyvaluepair<tkey, tvalue>>,  ienumerable<keyvaluepair<tkey, tvalue>>, ienumerable 

so, idictionary implements ienumerable<keyvaluepair<tkey, tvalue>> while igrouping implements ienumerable<telement>. if elements of igrouping contain keys, why interface not use keyvaluepair? seems methods implemented in idictionary useful igrouping such idictionary.containskey unavailable in igrouping, meaning attempt find key on group (in o(1) time) like:

list<int> mylist = new list<int>{ 1, 2, 3, 1}; var grp = mylist.groupby(x => x).todictionary(x => x.key, x => x.count()); if (grp.containskey(somevalue)){...} 

am using igrouping wrong? missing?

to find if particular igrouping<tkey, tvalue> contains particular tkey, check key property directly. no need loop.

groupby doesn't return igrouping, returns ienumerable<igrouping<...>>. is, igrouping represents results 1 single key value, , multiple such results. cannot return dictionary<tkey, tvalue>, groupby preserves key order, , dictionary doesn't. no other pre-existing collection type appropriate here.

since don't care key order, , don't care individual values each key (since they're identical), can store results in dictionary yourself, you're doing now. you're doing right thing.

if don't need counts, can use hashset<int>.

if end needing individual values, can use tolookup.