{"id":11958,"date":"2022-09-29T03:25:42","date_gmt":"2022-09-28T21:55:42","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-c-hashset-init-takes-too-long\/"},"modified":"2022-09-29T03:25:42","modified_gmt":"2022-09-28T21:55:42","slug":"solved-c-hashset-init-takes-too-long","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-c-hashset-init-takes-too-long\/","title":{"rendered":"[Solved] c# HashSet init takes too long"},"content":{"rendered":"

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If I stay away from the fact if using the HashSet is the right type for the job at hand or if your Comparer even makes sense implementing a proper GetHashCode<\/code> does seem to make a huge difference.<\/p>\n

Here is an example implementation, based on an answer from Marc Gravell:<\/p>\n

class KeyWordComparer : EqualityComparer<Keyword>\n{\n    \/\/ omitted your Equals implentaton for brevity\n\n    public override int GetHashCode(Keyword keyword)\n    {\n        \/\/return 0; \/\/ this was the original\n        \/\/ Marc Gravell https:\/\/stackoverflow.com\/a\/371348\/578411\n        int hash = 13;\n        \/\/ not sure what is up with the only 8 ID's but I take that as a given\n        for(var i=0; i < Math.Min(keyword._lista_modelos.Count, 8) ; i++)\n        {\n            hash = (hash * 7) + keyword._lista_modelos[i].GetHashCode();\n        }\n        return hash;\n    }\n}\n<\/code><\/pre>\n
When I run this in LinqPad with this test rig<\/p>\n
   Random randNum = new Random();\n   var kc = new KeyWordComparer();\n   HashSet<Keyword> set = new HashSet<Keyword>(kc);\n   var sw = new Stopwatch();\n   sw.Start();\n   for(int i =0 ; i< 10000; i++)\n   {\n     set.Add(new Keyword(Enumerable\n            .Repeat(0, randNum.Next(1,10))\n            .Select(ir => randNum.Next(1, 256)).ToList()));\n   }\n   sw.Stop();\n   sw.ElapsedMilliseconds.Dump(\"ms\");\n<\/code><\/pre>\n
this is what I measure:<\/p>\n