c# - Getting a sub set of SortedDictionary as a SortedDictionary -

in c# how filter sorteddictionary using linq producing subset sorteddictionary? eg. i'd write

sorteddictionary<int, person> source = ..fetch.. sorteddictionary<int, person> filtered = source.where(x=>x.foo == bar) 

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the way i've found create helper method , use that

sorteddictionary<tkey, tvalue> subdictionary<tkey, tvalue> ienumerable<keyvaluepair<tkey, tvalue>> l)  {     sorteddictionary<tkey, tvalue> result = new sorteddictionary<tkey, tvalue>();     foreach (var e in l)       result[e.key] = e.value;     return result; }  ...  sorteddictionary<int, person> source = ..fetch.. sorteddictionary<int, person> filtered = subdictionary(source.where(x=>x.foo == bar)) 

if want one-statement solution, work:

sorteddictionary<int, person> filtered =      new sorteddictionary<int, person>(         source.where(x => x.value.foo == bar)               .todictionary(kvp => kvp.key, kvp => kvp.value)); 

however, inefficient, creates 2 dictionary objects (the todictionary() extension method creates one, passed sorteddictionary constructor).

your helper method result in better performance. cleaner syntax, make extension method on ienumerable<keyvaluepair<tkey, tvalue>>:

public static class keyvaluepairenumerableextensions {     public static sorteddictionary<tkey, tvalue> tosorteddictionary<tkey, tvalue>(         ienumerable<keyvaluepair<tkey, tvalue>> l)     {         sorteddictionary<tkey, tvalue> result = new sorteddictionary<tkey, tvalue>();         foreach (var e in l)              result[e.key] = e.value;         return result;     } } 

which can used this:

var f2 = source.where(x => x.value.foo == bar).tosorteddictionary();