Question

I have two dictionaries in c#.

The Two Dictionaries and their calues are

 Dictionary<int,List<string>> D1 = new Dictionary<int,List<string>>(); 
 Dictionary<int,List<string>> D2= new Dictionary<int,List<string>>(); 
 Dictionary<int,List<string>> D3 new Dictionary<int,List<string>>();
 D1[1] = new List<string>{"a","b"};
 D1[2] = new List<string>{"c","d"}; 
 D1[3] = new List<string>{"e","f"}; 
 D1[4] = new List<string>{"h"};  

Where 1,2,3 and 4 are keys of Dictionary D1

 D2[1] = new List<string>{"a","b"}; 
 D2[2] = new List<string>{"c","d"}; 
 D2[3] = new List<string>{"e","f"};
 D2[4] = new List<string>{"g"}; 
 D2[5] = new List<string>{"b","h"};
 D2[6] = new List<string>{"f","l"};
 D2[7] = new List<string>{"z"}; 

Where 1,2,3,4,5,6 and 7 are keys of Dictionary D2

Then the output Dictionary Contains this values,

 D3[1] = {"a","b","h"}   D3[2] = {"c","d"}   D3[3] = {"e","f","l"} 

Note: Please take the Input Dictionary with values greater than 1.Thats why i am eliminating the D1[4] , D2[4] and D2[7]

IS IT POSSIBLE TO MERGE IT USING LINQ?

Answer 1

Yes it’s possible but it’s not pretty!

//firstly lets get the keys that are valid (i.e. have more than one element in their list)
var validD1Elements = D1.Where(d => d.Value.Count > 1);
var validD2Elements = D2.Where(d => d.Value.Count > 1);

//merge the valid keys together so we know which ones we want to select
var mergedKeys = validD1Elements.Select(d => d.Key).Union(validD2Elements.Select(d => d.Key));

//perform the merge
var mergeResult = mergedKeys.Select (key => new
{
    Key = key,
    //select the values from D1
    Value = validD1Elements.Where(d => d.Key == key).SelectMany(d => d.Value)
    //concat the values from D2
    .Concat(validD2Elements.Where(d => d.Key == key).SelectMany(d => d.Value))
}).ToDictionary(e => e.Key, e => e.Value);

This merge uses Concat so you will get duplicates, i.e. mergeResult[1] will be { "a", "b", "a", "b" }.

If you do not want duplicates change the following code from this:

//concat the values from D2
.Concat(validD2Elements.Where(d => d.Key == key).SelectMany(d => d.Value))

to this:

//union the values from D2
.Union(validD2Elements.Where(d => d.Key == key).SelectMany(d => d.Value))

mergeResult[1] will then be { "a", "b" }.