My Point of View

I am receiving this dataset from a remote server;

TagNumber	TagCode	CageNumber	FoodType	FoodValue
A-2021-1	WHITE	A9:I10	        Milk	        A11:I
A-2021-1	WHITE	A9:I10	        Corn	        A10:I
A-2021-1	RED	A11:I13	        Meat	        B1:B2
A-2021-1	RED	A11:I13	        Hay	        A14:I
A-2021-1	GREEN	A8:J9	        Milk	        B1:B2
A-2021-1	GREEN	A8:J9	        Milk	        A10:J

I need to create this object, a complex type;

public class Animal
{
    public string TagNumber { get; set; }
    public string TagCode { get; set; }
    public string CageNumber { get; set; }
    public List<AnimalFood> Food { get; set; }
}

public class AnimalFood
{
    public string FoodType { get; set; }
    public string FoodValue { get; set; }
}

There could be many ways to handle this. This is one of them;

Create a dictionary object using LINQ GroupBy and TagCode column from incoming dataset;

var allAnimals = animalData
    .GroupBy(item => item.TagCode)
    .ToDictionary(grp => grp.Key, grp => grp.ToList());

Create unique animals out of dictionary object;

var uniqueAnimals = allAnimals.Keys.Distinct().ToList();

Create the object (animal) and add them to zoo :);

var zoo = new List<Animal>();
foreach (string animal in uniqueAnimals)
{
    var animalRow = allAnimals[animal];
    var animalRowFirst = animalRow.FirstOrDefault();
    var animalRecord = new Animal
    {
         TagNumber = animalRowFirst.TagNumber,
         TagCode = animalRowFirst.TagCode,
         CageNumber = animalRowFirst.CageNumber
    };
    //time for food
    var animalFood = new List<AnimalFood>();
    foreach(var item in animalRow)
    {
        item.Food.ForEach(x =>
        {
            animalFood.Add(new AnimalFood
            {
                  FoodType = x.FoodType,
                  FoodValue = x.FoodValue
            });
        });
    }
   //this is our custom type
   animalRecord.Food = animalFood;
   zoo.Add(animalRecord);
}

Sample output;

It’s easier to apply different filters on this object;

var animalFilter = zoo.Where(x => x.TagCode.ToUpper() == "WHITE");

Resources

https://stackoverflow.com/questions/3186818/unique-list-of-items-using-linq

C# provides various ways to check for a null object.

Let’s create a class to test;

public class UserObject
{
    public int Id { get; set; }
    public string? Name { get; set; }
}

The most conventional way to check for null is by equating the object with null.

UserObject userObject = null;
//Conventional way to check for null
if (userObject == null)
{
    userObject = new UserObject();
    Console.WriteLine("userObject null - handled using conventional manner");
}

if (userObject != null)
{
    Console.WriteLine("userObject not null - handled using conventional manner");
}

C#7 introduced a new way to write the above code in a more readable way by using the is keyword.

//C#7 introduces a new way 
userObject = null;
if (userObject is null)
{
    userObject = new UserObject();
    Console.WriteLine("userObject null - handled using c#7");
}

The same code can be written using null-coalescing operator.

//we can write the same code using null-coalescing operator
userObject = null;
userObject = userObject ?? new UserObject();
Console.WriteLine("userObject null - handled using null-coalescing operator");

C#9 introduced a new way to write the above code in a more readable way by using the is not keyword.

//C#9 introduces a new way 
if (userObject is not null)
{
    userObject = new UserObject();
    Console.WriteLine("userObject not null - handled using c#9");
}

Hope, this helps.