Welcome to part 13 of my C# Tutorial. This time I’ll cover multiple functions you can use to work with lists of data including Lambda, Where, ToList, Select, Zip, Aggregate and Average. These tools are extremely powerful and they help you solve extremely complex problems easily.

For best results take notes on the cheat sheet provided below as you watch and leave any questions you have.

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Code & Transcript

using System;
using System.Linq;
using System.Collections.Generic;

namespace CSharpTutA.cs
{
    // This time I'll cover multiple functions 
    // you can use to work with lists of data
    // including Lambda, Where, ToList, Select,
    // Zip, Aggregate and Average

    class Program
    {
        // Delegate that is assigned a Lambda
        // expression
        delegate double doubleIt(double val);

        static void Main(string[] args)
        {
            // Like we did with predicates earlier
            // Lambda expressions allow you to 
            // use anonymous methods that define
            // the input parameters on the left 
            // and the code to execute on the right

            // Assign a Lambda to the delegate
            doubleIt dblIt = x => x * 2;
            Console.WriteLine($"5 * 2 = {dblIt(5)}");

            // You don't have to use delegates though
            // Here we'll search through a list to 
            // find all the even numbers
            List<int> numList = new List<int> { 1,9,2,6,3 };

            // Put the number in the list if the 
            // condition is true
            var evenList = numList.Where(a => a % 2 == 0).ToList();

            foreach (var j in evenList)
                Console.WriteLine(j);

            // Add values in a range to a list
            var rangeList = numList.Where(x => (x > 2) || (x < 9)).ToList();

            foreach (var k in rangeList)
                Console.WriteLine(k);

            // Find the number of heads and tails in
            // a list 1 = H, 2 = T

            // Generate our list
            List<int> flipList = new List<int>();
            int i = 0;
            Random rnd = new Random();
            while (i < 100)
            {
                flipList.Add(rnd.Next(1, 3));
                i++;
            }

            // Print out the heads and tails
            Console.WriteLine("Heads : {0}",
                flipList.Where(a => a == 1).ToList().Count());
            Console.WriteLine("Tails : {0}",
                flipList.Where(a => a == 2).ToList().Count());

            // Find all names starting with s
            var nameList = new List<string> { "Doug", "Sally", "Sue" };

            var sNameList = nameList.Where(x => x.StartsWith("S"));

            foreach (var m in sNameList)
                Console.WriteLine(m);

            // ---------- SELECT ----------
            // Select allows us to execute a function 
            // on each item in a list

            // Generate a list from 1 to 10
            var oneTo10 = new List<int>();
            oneTo10.AddRange(Enumerable.Range(1, 10));

            var squares = oneTo10.Select(x => x * x);

            foreach (var l in squares)
                Console.WriteLine(l);

            // ---------- ZIP ----------
            // Zip applies a function to two lists 
            // Add values in 2 lists together
            var listOne = new List<int>(new int[] { 1, 3, 4});
            var listTwo = new List<int>(new int[] { 4, 6, 8});

            var sumList = listOne.Zip(listTwo, (x, y) => x + y).ToList();

            foreach (var n in sumList)
                Console.WriteLine(n);

            // ---------- AGGREGATE ----------
            // Aggregate performs an operation on 
            // each item in a list and carries the 
            // results forward 

            // Sum values in a list
            var numList2 = new List<int>() { 1, 2, 3, 4, 5 };
            Console.WriteLine("Sum : {0}", 
                numList2.Aggregate((a, b) => a + b));

            // ---------- AVERAGE ----------
            // Get the average of a list of values
            var numList3 = new List<int>() { 1, 2, 3, 4, 5 };

            // AsQueryable allows you to manipulate the
            // collection with the Average function
            Console.WriteLine("AVG : {0}", 
                numList3.AsQueryable().Average());

            // ---------- ALL ----------
            // Determines if all items in a list
            // meet a condition
            var numList4 = new List<int>() { 1, 2, 3, 4, 5 };

            Console.WriteLine("All > 3 : {0}", 
                numList4.All(x => x > 3));

            // ---------- ANY ----------
            // Determines if any items in a list
            // meet a condition
            var numList5 = new List<int>() { 1, 2, 3, 4, 5 };

            Console.WriteLine("Any > 3 : {0}",
                numList5.Any(x => x > 3));

            // ---------- DISTINCT ----------
            // Eliminates duplicates from a list
            var numList6 = new List<int>() { 1, 2, 3, 2, 3 };

            Console.WriteLine("Distinct : {0}",
                string.Join(", ", numList6.Distinct()));

            // ---------- EXCEPT ----------
            // Receives 2 lists and returns values not
            // found in the 2nd list
            var numList7 = new List<int>() { 1, 2, 3, 2, 3 };
            var numList8 = new List<int>() { 3 };

            Console.WriteLine("Except : {0}",
                string.Join(", ", numList7.Except(numList8)));

            // ---------- INTERSECT ----------
            // Receives 2 lists and returns values that
            // both lists have
            var numList9 = new List<int>() { 1, 2, 3, 2, 3 };
            var numList10 = new List<int>() { 2, 3 };

            Console.WriteLine("Intersect : {0}",
                string.Join(", ", numList9.Intersect(numList10)));

            Console.ReadLine();

        }

    }

}