Question

I have a List of String like

List<String> MyList=new List<String>{"A","B"};

and a

Dictionary<String, Dictionary<String,String>> MyDict=new Dictionary<String,Dictionary<String,String>>(); 

which contains

 Key      Value
          Key     Value

   "ONE"        "A_1"  "1"
                "A_2"  "2"
                "X_1"  "3"
                "X_2"  "4"
                "B_1"  "5"

    "TWO"       "Y_1"  "1"
                "B_9"  "2"
                "A_4"  "3"
                "B_2"   "6"
                "X_3" "7"

I need to merge the the list and Dictionary into a new Dictionary

 Dictionary<String,String> ResultDict = new Dictionary<String,String>()

The resulting dictionary contains

Key Value

"A_1"   "1"
"A_2"   "2"
"B_1"   "5"
"A_4"   "3"
"B_2"   "6"
"X_2"   "4"
"X_3"   "7"

Merge rule

1. First add the items which has a substring equals to any item in the list.
2. Then Merge the items in the “MyDict” so the result should not contain duplicate keys as well as duplicate values.

Here is my source code.

        Dictionary<String, String> ResultDict = new Dictionary<string, string>();
        List<String> TempList = new List<string>(MyDict.Keys);
        for (int i = 0; i < TempList.Count; i++)
        {
            ResultDict = ResultDict.Concat(MyDict[TempList[i]])
                                              .Where(TEMP => MyList.Contains(TEMP.Key.Contains('_') == true ? TEMP.Key.Substring(0, TEMP.Key.LastIndexOf('_'))
                                                                                                            : TEMP.Key.Trim()))
                                              .ToLookup(TEMP => TEMP.Key, TEMP => TEMP.Value)
                                              .ToDictionary(TEMP => TEMP.Key, TEMP => TEMP.First())
                                              .GroupBy(pair => pair.Value)
                                              .Select(group => group.First())
                                              .ToDictionary(pair => pair.Key, pair => pair.Value);            }
        for (int i = 0; i < TempList.Count; i++)
        {
            ResultDict = ResultDict.Concat(MyDict[TempList[i]])
                                              .ToLookup(TEMP => TEMP.Key, TEMP => TEMP.Value)
                                              .ToDictionary(TEMP => TEMP.Key, TEMP => TEMP.First())
                                              .GroupBy(pair => pair.Value)
                                              .Select(group => group.First())
                                              .ToDictionary(pair => pair.Key, pair => pair.Value);
        }

its working fine, but I need to eliminate the two for loops or at least one
(Any way to do this using LINQ or LAMBDA expression)

Answer 1

Here’s one way you could do it with LINQ and lambdas, as requested:

var keysFromList = new HashSet<string>(MyList);
var results =
    MyDict.Values
          .SelectMany(x => x)
          .OrderBy(x => {
                            int i = x.Key.LastIndexOf('_');
                            string k = (i < 0) ? x.Key.Trim() 
                                               : x.Key.Substring(0, i);
                            return keysFromList.Contains(k) ? 0 : 1;
                        })
          .Aggregate(new {
                             Results = new Dictionary<string, string>(),
                             Values = new HashSet<string>()
                         },
                     (a, x) => {
                                   if (!a.Results.ContainsKey(x.Key)
                                           && !a.Values.Contains(x.Value))
                                   {
                                       a.Results.Add(x.Key, x.Value);
                                       a.Values.Add(x.Value);
                                   }
                                   return a;
                               },
                     a => a.Results);