Grouping a list of objects by property, divided into several lists.

Question

Current structure (cannot be changed due to system requirements)

class Statement
{
    string section;
    string category;
    string statement;
}

List of notes

section      category     statement
1            a            apple
1            a            banana
1            b            potato
2            c            car
2            c            bus
2            d            plane

Problem

I start with List<Statement>and you need to break them down based on the section, and then the category into the following (or similar) structure

struct SectionCollection
{
    string sectionName {get{return categories[0].section;}}
    List<CategoryCollection> categories;
}

struct CategoryCollection
{
    string categoryName {get{return statements[0].category;}}
    List<Statement> statements;
}

So, from List<Statement>I must have List<SectionCollection>, within which is List<CategoryCollection>, within which there is List<Statement>

So, in the above data example, I would have

• List<SectionCollection>
  • List<CategoryCollection> (inside)
    • List<Statement> (inside)

Notes

It is possible that the operator A or the category may be the same in another section - they should still belong in different SectionCollections

Attempt

, , . , - , , .

var sections = statements.GroupBy(x => x.section).Select(y => y.ToList()).ToList();
foreach(var section in sections)
{
     SectionCollection thisSection = new SectionCollection();
     var categories = section.GroupBy(x => x.category).Select(y => y.ToList()).ToList();

    foreach(var category in categories)
    {
        thisSection.categories.Add(new CategoryCollection({statements = category});
    }
}

Answer 1

, , , Categories SectionCollection.

:

SectionCollection thisSection = new SectionCollection();

To:

SectionCollection thisSection = new SectionCollection() 
{ 
    Categories = new List<CategoryCollection>() 
};

. , , :

var sections = statements.GroupBy(x => x.Section).Select(y => y.ToList()).ToList();

var result = new List<SectionCollection>();

foreach (var section in sections)
{
    SectionCollection thisSection = new SectionCollection() { Categories = new List<CategoryCollection>() };

    var categories = section.GroupBy(x => x.Category).Select(y => y.ToList()).ToList();

    foreach (var category in categories)
    {
        thisSection.Categories.Add(new CategoryCollection { Statements = category });
    }

    result.Add(thisSection);
}

, , - :

internal class Program
{
    static void Main(string[] args)
    {
        var statements = new List<Statement>()
        {
            new Statement(1, "a", "apple"),
            new Statement(1, "a", "banana"),
            new Statement(1, "b", "potato"),
            new Statement(2, "c", "car"),
            new Statement(2, "c", "bus"),
            new Statement(2, "d", "plane")
        };

        var sectionCollections = statements
            .GroupBy(s => s.Section)
            .Select(group => new SectionCollection(group.Key, statements))
            .ToList();
    }

    public class Statement
    {
        public Statement(int section, string category, string statementName)
        {
            Section = section;
            Category = category;
            StatementName = statementName;
        }

        public int Section { get; }

        public string Category { get; }

        public string StatementName { get; }
    }

    public class SectionCollection
    {
        public SectionCollection(int sectionName, List<Statement> statements)
        {
            SectionName = sectionName;

            Categories = statements
                .Where(s => s.Section == sectionName)
                .GroupBy(s => s.Category)
                .Select(group => new CategoryCollection(group.Key, group.ToList()))
                .ToList();
        }

        public int SectionName { get; }

        public List<CategoryCollection> Categories { get; }
    }

    public class CategoryCollection
    {
        public CategoryCollection(string categoryName, List<Statement> statements)
        {
            CategoryName = categoryName;
            Statements = statements;
        }

        public string CategoryName { get; }

        public List<Statement> Statements { get; }
    }
}

:

Answer 2

SectionCollection :

SectionCollection thisSection = new SectionCollection();

thisSection.categories new - , .

, thisSection.categories.Add , .