My question is about comparing List<string> with Dictionary <string, List<string>> using C# linq

Question

I have referred the below link in stack-overflow for my requirement which provide the matching key and Boolean results.I need the result of keys and values from the dictionary which matches with list of string.

Referred Link below: Array with Dictionary in c# using Linq

The example is provided in the same link above. Any how I will provide the same below

Dictionary<int, List<string>> dict = new Dictionary<int, <string>>
{ 
    {1, new List<string>(){"A","B"}},
    {2, new List<string>(){"C","D"}},
    {3, new List<string>(){"G","H"}},
    {4, new List<string>(){"E","F"}},
    {5, new List<string>(){"I","J"}},
};

string[] values = new [] 
{
    "A", "D", "E"
};

var result = 
  from kvp in dict
  join s in values on kvp.Value equals s
select new {kvp.Key, Found = true};

What I tried is below:

var result = dict
  .Select(x => new { 
     keys = x.Key, 
     values = values
       .ToList()
       .Any(x.Value.Contains) 
   });

I Expect the output be like {1,A},{2,D},{4,E} but actually coming {1,True},{4,True},{5,True}

Could some one help me on this.

Answer 1

Technically, if you want, say, List<object> == {1, "A", 4, "D", 5, "E"};

I Expect the output be like {1,A,4,D,5,E}

you can try Where to filter out dict records and SelectMany to flatten them:

  Dictionary<int, string> dict = new Dictionary<int, string>() { 
    {1, new "A"},
    {2, new "B"},
    {3, new "c"},
    {4, new "D"},
    {5, new "E"},
  };

  string[] values = new [] {"A", "D", "E"};

  var result = dict
    .Where(pair => values.Contains(pair.Value))
    .SelectMany(pair => new object[] { pair.Key, pair.Value})
    .ToList();

  Console.Write(string.Join(", ", result));

Outcome:

  1, A, 4, D, 5, E

However, I doubt if you really want such strange data representation. A filtered collection (or dictionary) without SelectMany is more convenient:

  List<KeyValuePair<int, string>> result = dict
    .Where(pair => values.Contains(pair.Value))
    .ToList();

  Console.Write(string.Join(", ", result.Select(pair => $"{pair.Key}, {pair.Value}")));

Or

  Dictionary<int, string> result = dict
    .Where(pair => values.Contains(pair.Value))
    .ToDictionary(pair => pair.Key, pair => pair.value);

  Console.Write(string.Join(", ", result.Select(pair => $"{pair.Key}, {pair.Value}")));

Which produce the same outcome:

  1, A, 4, D, 5, E

Edit: Well, the problem's changed dramatically. Now we have

  Dictionary<int, List<string>> dict = new Dictionary<int, <string>>() { 
    {1, new List<string>() {"A", "B"}},
    {2, new List<string>() {"C", "D"}},
    {3, new List<string>() {"G", "H"}},
    {4, new List<string>() {"E", "F"}},
    {5, new List<string>() {"I", "J"}},
  };

  string[] values = new [] { "A", "D", "E" };

And we want filtered Dictionary<int, List<string>>:

  var result = dict
    .Select(pair => new {
      key = pair.Key,
      value = pair.Value.Intersect(values).ToList()
    })
    .Where(item => item.value.Any())
    .ToDictionary(item => item.key, item => item.value);

  Console.Write(string.Join(Environment.NewLine, result
    .Select(pair => $"{pair.Key} : [{string.Join(", ", pair.Value)}]"))); 

Outcome:

1 : [A]
2 : [D]
4 : [E]