Question

Let’s say I have a list of unknown number of elements in string value, I want to divide it to n subarray or lists (n could be any int, for example n=3), what is best way to do it?

note: the number of elements in each group is not necessary to be equal

Answer 1

LINQ GroupBy and Select methods can help:

var list = new List<string>() { "A", "B", "C", "D", "E", "F", "G" };
int groupCount = 3;

var subLists = list.Select((s, i) => new {Str = s, Index = i}).
                    GroupBy(o => o.Index % groupCount, o => o.Str).
                    Select(coll => coll.ToList()).
                    ToList();

This code will result in subLists containing a list of three List<string> collections: {"A", "D", "G"}, {"B", "E"} and {"C", "F"}. In order to achieve that I based my grouping on element indices in the original list (there is an overload for Select method that lets you do that, see link above). You can use some other logic to select the key.

In my example subLists is a List<List<string>>. If you need an array, use ToArray where appropriate.

EDIT: using modulo operation for grouping may not be a good idea if you care about the way values are distributed between lists. Probably the better option is to do it this way:

var list = new List<string>() { "A", "B", "C", "D", "E", "F", "G" };
int groupCount = 3;

int maxPerGroup = (int)Math.Ceiling((double)list.Count / groupCount);

var subLists = list.Select((s, i) => new {Str = s, Index = i}).
                    GroupBy(o => o.Index / maxPerGroup, o => o.Str).
                    Select(coll => coll.ToList()).
                    ToList();

This will produce the following result: {"A", "B", "C"}, {"D", "E", "F"}, {"G"} which may be more sane way to distribute the values.

Bottom line is, you can achieve what you need by using GroupBy and Select methods, just provide the correct grouping logic that is suitable for your domain.