Split dictionary into multiple equal sized dictionaries

Question

I have a Dictionary shown below. Say there are 400 elements in the Dictionary I want to split this Dictionary into 4 equal sized dictionaries. How do I do this? With list there is a range method that I can use however not sure what to do here?

I do not care how the Dictionary is split just so that they are equally sized.

Dictionary<string, CompanyDetails> coDic;

Answer 1

I would use the following query:

Dictionary<string, CompanyDetails>[] result =
    dict
        .Select((kvp, n) => new { kvp, k = n % 4 })
        .GroupBy(x => x.k, x => x.kvp)
        .Select(x => x.ToDictionary(y => y.Key, y => y.Value))
        .ToArray();

The advantage here is the avoidance of closing over a counter as the .Select((kvp, n) => ...) statement has a counter built-in.

Answer 2

You can use a simple modulus to group the dictionary in parts:

int numberOfGroups = 4;
int counter = 0;

var result = dict.GroupBy(x => counter++ % numberOfGroups);

The modulus (%) makes the GroupBy to be restricted to a number in the range 0..3 (actually 0..numberOfGroups - 1). This will make the grouping for you.

A problem though with this one is that it doesn't preserve the order. This one does:

decimal numberOfGroups = 4;
int counter = 0;
int groupSize = Convert.ToInt32(Math.Ceiling(dict.Count / numberOfGroups));

var result = dict.GroupBy(x => counter++ / groupSize);