Random C#

Vertical List

///<summary>
/// Returns a dictionary of lists keyed by row index. 
/// Each list in the dictionary corresponds to a row of values.
/// "kvp" stands for "key-value pair".
///</summary>
public class ListHelper 
{
  public static Dictionary<int, List<T>> ToVertical<T>(IEnumerable<T> list, int maxColumns) {
    if(list == null) {
      throw new ArgumentNullException("list");
    }

    if(list.Count() < 1) {
      throw new ArgumentException("`list` must contain one or more values.");
    }

    if(maxColumns < 1) {
      throw new ArgumentException("`maxColumns` should be one or greater.");
    }

    var verticalDictionary = new Dictionary<int, List<T>>();
    var rows = (int)Math.Ceiling((double)(list.Count())/maxColumns); //Calculate the no. of rows.

    //Map the supplied list into a list of key-value-pairs.
    var kvps = list.Select((c, index) => {
     return new  { Key = index%rows, Value = c };
    });
  
    //Enumerate the key-value-pairs from the previous step and place their values in the verticalDictionary.
    foreach(var kvp in kvps) {
      if(verticalDictionary.Any(k => k.Key == kvp.Key)) {
        verticalDictionary[kvp.Key].Add(kvp.Value);
      } else {
        verticalDictionary.Add(kvp.Key, new List<T> { kvp.Value });
      }
    }

    return verticalDictionary;
  }
}

//Example usage...

var countries = new string [] { "Angola", "Burundi", "Chile", "Denmark", "Estonia", "France", "Germany", "Holland", "India", "Jamaica", "Kiribati", "Laos", "Moldova" };
var maxColumns = 4;

var verticalValues = ListHelper.ToVertical(countries, maxColumns);
var maxKey = verticalValues.Max(kvp => kvp.Key);

for(int i = 0; i <=maxKey; i++) {
  Console.Write(String.Join(" | ", verticalValues[i]) + "\n");  
}