c# - Add objects to a List nested inside a Dictionary using LINQ extensions -

i have dictionary<t, t> contains key (that represents category) empty list<t> value:

dictionary<string, list<imyobject>> myobjects; 

each pair looks this:

{ firstcategory, new list<imyobject>> } 

i have list<t> of imyobject's:

list<imyobject> myobjectsunsorted; 

i want loop through myobjectsunsorted , add correct list<t>

foreach (var myobject in myobjectsunsorted) {     myobjects[myobject.category].add(myobject); } 

how can without loop? example linq extension method? other objects in example created .select() dosen't fit bill in last foreach.

i suggest using lookup instead:

ilookup<string, imyobject> lookup = myobjectsunsorted.tolookup(t => t.category); 

ilookup<,> precisely designed "multiple values per key" dictionary. being incredibly simple construct, has benefit if key isn't represented, empty sequence instead of exception. can always write:

foreach (var item in lookup[key]) {     ... } 

as opposed to:

ilist<myobject> list; if (dictionary.trygetvalue(key, out list)) {     foreach (var item in list)     {         ...     } } 

note lookup immutable in can't change items in after construction. (if items mutable reference types, can modify objects of course...) can blessing or curse, depending on situation...