Iterate through list of items to their parent and parent to parent level

Question

I have one requirement to iterate through list of items which has n-level of hierarchy and I would like to get bottom-up elements for the selected item ID.

For eg below is the raw data

ID         ParentID    ItemName       Category
1          -1          Chai           Breweries
4          -1          Mouse-pad      Electronic
3           1          GST            Taxes
2           1          Spices         
5           4          Mobile         
6           3          My Tax         

I want to program in C# to iterate and show for eg if I pass ID parameter for method 6 then it should print output as below

ParentID=3, Name=My Tax, Category=Taxes

If I pass ID parameter as 2 then output should be similar

ParentID=1, Name=Spices, Category=Breweries

please help me in achieving this functionality may be by using Generic collection or any algorithm would help

What I have tried is I have tried using List and plus LINQ's select many, but with this option I was able to fetch only current item, but not parent category value if current item do not have category associated to it. Also tried to add recursive method but not sure how to build end output, with recursive we should only get current item.

Okay as per below comments I have used recursive function as below

class Program
{
    static void Main(string[] args)
    {
        int categoryId = 202;
        var products = GetProducts();
        var product = products.FirstOrDefault(p => p.ID == categoryId);

        var output = GetProductRecursively(products, categoryId, string.Empty);
        Console.WriteLine(output);
        Console.Read();
    }

    public static string GetProductRecursively(List<Product> products, int parentId, string output)
    {
        var product = products.FirstOrDefault(p => p.ParentID == parentId);
        StringBuilder stringBuilder = new StringBuilder();
        if (string.IsNullOrEmpty(product.Category))
        {
            if (string.IsNullOrEmpty(output))
            {
                stringBuilder.Append($"ParentCategoryID={ product.ParentID}, Name={ product.ItemName}, Keywords=");
                GetProductRecursively(products, product.ParentID, stringBuilder.ToString());
            }
            else
                GetProductRecursively(products, product.ParentID, output);
        }
        else
            stringBuilder.Append($"{output}{product.Category}");
        return stringBuilder.ToString();
    }
    public static List<Product> GetProducts()
    {
        var products = new List<Product>();
        products.Add(new Product { ID = 1, ParentID = -1, ItemName = "Chai", Category = "Breweries" });
        products.Add(new Product { ID = 4, ParentID = -1, ItemName = "Mouse-pad", Category= "Electronic" });
        products.Add(new Product { ID = 3, ParentID  = 1, ItemName = "GST", Category= "Taxes" });
        products.Add(new Product { ID = 2, ParentID = 1, ItemName = "Spices" });
        products.Add(new Product { ID = 5, ParentID = 4, ItemName = "Mobile" });
        products.Add(new Product { ID = 6, ParentID = 3, ItemName = "My Tax" });
        return products;
    }
}

public class Product
{
    public int ID { get; set; }
    public int ParentID { get; set; }
    public string ItemName { get; set; }
    public string Category { get; set; }
}

However, in one iteration it returns Category for parentID, but as it's in recursion it keep on finish its job for earlier iteration hence at this point Category is all time returns ""(empty.string)

Answer 1

Non-recursive solution can look like this:

var productId = 6;
var products = GetProducts();

var productDict = products // create dictionary to search for products by id
    .GroupBy(p => p.ID)
    .ToDictionary(p => p.Key, g => g.First());

var product = productDict[productId];

// create loop state variables 
string category = null; 
var currProduct = product;
// cycle while category not found   
while (category == null)
{
    // or there is no parent product
    if (!productDict.ContainsKey(currProduct.ParentID))
    {
        break;
    }

    currProduct = productDict[currProduct.ParentID];
    category = currProduct.Category;
}

Console.WriteLine($"{category}-{product.ItemName}");

Answer 2

Without any code, I can only give you a "default" answer for your problem.

To solve your problem, you must implement a function in your classes to get the parent of your instance.

To get the absolute parent (object has no parent itself) you must implement a function which calls itself as long as it has a parent.

Answer 3

Ok finally got it working with correct logic, working code as below

class Program
{
    static void Main(string[] args)
    {
        int productId = 6;
        var products = GetProducts();
        var product = products.FirstOrDefault(p => p.ID == productId);

        var output = GetProductRecursively(products, productId, string.Empty);
        Console.WriteLine(output);
        Console.Read();
    }

    public static string GetProductRecursively(List<Product> products, int Id, string output)
    {
        var product = products.FirstOrDefault(p => p.ID == Id);
        StringBuilder stringBuilder = new StringBuilder();
        if (string.IsNullOrEmpty(output))
            output = stringBuilder.Append($"ParentCategoryID={ product.ParentID}, Name={ product.ItemName}, Keywords=").ToString();
        if (string.IsNullOrEmpty(product.Category))
        {
            return GetProductRecursively(products, product.ParentID, output);
        }
        else
            output += $"{product.Category}";
        return output;
    }
    public static List<Product> GetProducts()
    {
        var products = new List<Product>();
        products.Add(new Product { ID = 1, ParentID = -1, ItemName = "Chai", Category = "Breweries" });
        products.Add(new Product { ID = 4, ParentID = -1, ItemName = "Mouse-pad", Category = "Electronic" });
        products.Add(new Product { ID = 3, ParentID = 1, ItemName = "GST", Category = "Taxes" });
        products.Add(new Product { ID = 2, ParentID = 1, ItemName = "Spices" });
        products.Add(new Product { ID = 5, ParentID = 4, ItemName = "Mobile" });
        products.Add(new Product { ID = 6, ParentID = 3, ItemName = "My Tax" });
        return products;
    }
}

public class Product
{
    public int ID { get; set; }
    public int ParentID { get; set; }
    public string ItemName { get; set; }
    public string Category { get; set; }
}