Collection Classes

Introduction

CONCEPT: This concept is an extension to that of Arrays. The collection class used will be the generic list, List<T>. This is a strongly typed list that has built-in methds for sorting, searching, and modifying the contents of the list.

List

The <T> is stands for any Type of object.

The List<T> has the following properties:

• .Count: allows you to display the number of objects in the list.

The List<T> has the following methods:

• .Add(): allows you to add a new object to the end of the list
• .Clear(): allows you to delate all the objects in the list
• .Find(): allows you to find the first item in the list that matches the search criteria
• .FindIndex(): allows you to find the index of the object that matches the search criteria
• .Remove(): allows you remove the first occurence of the object in the list
• .RemoveAt(): allows you to remove an object from the list at a specified index
• .Sort(): allows you to sort the list; this requires a different technique from sorting an array

Note: Adding or removing an object from a list will automatically change the .Count property.

Useful Code

Lambda Sort

employees.Sort((e1, e2) => e1.DOB.CompareTo(e2.DOB));

List Demo Methods

static void DisplayList(List<string> classNames)
{
    int row = 1;
    Console.ForegroundColor = ConsoleColor.DarkMagenta;
    Console.WriteLine(" Names List:\n ----------------");
    foreach (string name in classNames)
    {
        if (row % 2 != 0)
        {
            Console.ForegroundColor = ConsoleColor.Blue;
        }
        else
        {
            Console.ForegroundColor = ConsoleColor.DarkRed;
        }
        Console.WriteLine("{0,3}. {1}", row, name);
        row++;
    }//end foreach
    Console.ForegroundColor = ConsoleColor.DarkMagenta;
    Console.WriteLine(" ----------------\n");
    Console.WriteLine("There are {0} students in this class", classNames.Count());
}//eom

static void RemoveElement(List<string> classNames, int location)
{
    classNames.RemoveAt(location - 1); // only because the row = index + 1
}//eom

static void RemoveElement(List<string> classNames, string searchName)
{
    int index = SearchList(classNames, searchName);
    if(index >= 0)
    {
        classNames.Remove(searchName);
    }
}//eom

static int SearchList(List<string> classNames, string searchName)
{
    //If found will return a valid index, else will return -1
    //Here we are using a Lambda expression you do not need to
    // know how these work, just that they do.
    return classNames.FindIndex(item => item.Equals(searchName));
}//eom

static void AddName(List<string> classNames)
{
    string name = GetValidName("Enter your full name: ");
    classNames.Add(name);
}//eom

static void SortList(List<string> names)
{
    int minIndex;
    string minValue, temp;
    for(int startScan = 0; startScan < names.Count - 1; startScan++)
    {
        minIndex = startScan;
        minValue = names[startScan];
        for(int index = startScan; index < names.Count; index++)
        {
            if(names[index].CompareTo(minValue) < 0)
            {
                minValue = names[index];
                minIndex = index;
                // now swap
                temp = names[minIndex];
                names[minIndex] = names[startScan];
                names[startScan] = temp;
            }
        }
    }
}//eom

Advanced Topics

Reading a file to List<T>
Writing List<T> to File
Dictionary List
ArrayList

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