Merge three dictionary with Linq-Union

i need to merge three dictionary collection, if key is same i want to add value.

Result is like 
One  - 5+5 =10  
two  - 10+20=30
three - 7
four  - 2
five  - 8
six   - 2


             Dictionary<string, int> d1 = new Dictionary<string, int>();
             d1.Add("one", 5);
             d1.Add("two", 10);
             d1.Add("three", 7);

             Dictionary<string, int> d2 = new Dictionary<string, int>();
             d2.Add("four", 2);
             d2.Add("two", 20);
             d2.Add("five", 8);

             Dictionary<string, int> d3 = new Dictionary<string, int>();
             d3.Add("one", 5);
             d3.Add("six", 2);

Union: ignore the matching resultset.

var uQuery = (开发者_高级运维from a in d1 select a).Union(from b in d2 select b).GroupBy(grp=>grp.Key );

You should use Concat instead of Union. Union will treat the key value pair ["one", 5] as duplicated in d1 and d3, and therefore exclude one instance of it, giving this result:

• "one", 5
• "two", 30
• "three", 7
• "four", 2
• "five", 8
• "six", 2

var result = d1.Concat(d2.Concat(d3)).GroupBy(keyValuePair => keyValuePair.Key).ToDictionary(group => group.Key, grp => grp.Sum(kvp => kvp.Value));

or perhaps more readably:

var union = d1.Concat(d2.Concat(d3));
var groupBy = union.GroupBy(keyValuePair => keyValuePair.Key);
var result = groupBy.ToDictionary(group => group.Key, grp => grp.Sum(kvp => kvp.Value));