Split dictionary into multiple dictionaries

Dictionary is the generic collection of key-value pairs and belongs to System.Collection.Generic namespace.

The .Net framework does not provide any built-in method to split the dictionary object into multiple dictionary objects of predefined sizes. So it can be achieved only by writing custom code that can break the dictionary into smaller pieces.

Let us consider a requirement to split a dictionary object having 31 key-value pairs into multiple dictionaries with each dictionary having 5 key-value pairs. Below code snippet breaks the dictionary into 7 chunks having 5, 5, 5, 5, 5, 5, 1 key-value pairs and adds them into List collection:

private List<string, string> SplitDictionary(IDictionary<string, string> dict, int size)
{
   int counter = 0;
   List<Dictionary<string, string>> result = dict
      .GroupBy(x => counter++ / size)
      .Select(g => g.ToDictionary(h => h.Key, h => h.Value)
      .ToList();
   return result;
}

With the help of foreach loop we can pick each chunk and do further processing or pass it as a parameter to any method.

We can directly pass the dictionary chunk to any method as a value type but cannot pass as a reference type. It is because the dictionary chunk is created from foreach loop and hence is not mutable.

Each dictionary chunk can be converted to a reference type by assigning it to a new dictionary object and then use a new dictionary object as a reference type.

Let us consider a dictionary object named "results" having IDictionary<string, string> signature. This code snippet can be used to pass the dictionary chunks to any method as reference type:

List<Dictionary<string, string>> chunks = SplitDictionary(results, 5);
foreach (var chunk in chunks)
{
   Dictionary<string, string> intermediate = chunk;
   CustomMethod(ref intermediate);
}

The intermediate object above uses the dictionary chunks as a reference type.