c# make elements of list of string unique, by appending variable number of spaces

Question

I have a little algorithm issue and I'm stuck for a (fast) implementation. Actually mine is unfinished, but is already slowing down the load of DataGridView.

Initial problem: The DataGridView of WinForms has a bug from 2005 (apparently still unsolved up to VS2015) that makes incorrect bound of columns having the same name case in-sensitive. More precise if you have 2 columns "Cat" and "cat" they will bound both to the same (first found) object in database.

Anyhow, I am using ITypedList and GetItemProperties() to inform DGV for fields that I want to link. The idea (seen somewhere on stackoverflow) is to add spaces after name of "duplicate case in-sensitive" columns like this:

"cat"   --> leave as is
"Cat"   --> needs to be come "Cat_"   _ means space
"cAt"   --> needs to become "cAt__"   __ means two spaces and so on

Algorithm problem: Add strings in a list with a loop. Before add, check if the string exists (trim and case insensitive) and if so, append a space to end of name. Leave the name unchanged as case. In other words, make strings unique by append n spaces to names.

Hope I described well, any idea appreciated.

I've done some tests with my variant and speed suffers, perhaps also do to the fact that DGV is firing GetItemProperties() callback 5 times or more.

Here is my code:

   public partial class Form1 : Form
    {

        List<string> list = new List<string>
        {
            "cat",      // the cat
            "Cat",      // first duplicate needs to become Cat_ (one space)
            "kitty",
            "kittY",
            "dog",
            "cAt",      // third duplicate needs to become cAt__ (two spaces)
            "Dog",
            "monkey",
            "monKey",
            "Monkey",
        };

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            AnimalHeaders phList = new AnimalHeaders();

            for (int i = 0; i < list.Count(); i++)
            {
                string field = list.ElementAt(i);

                var caseInsenList = phList.Where(z => z.Name.Trim().Equals(field, StringComparison.OrdinalIgnoreCase));

                int count = caseInsenList.Count();

                if (count == 0) // no results
                {
                    phList.Add(new AnimalHeader { Name = field });
                }
                else // exists but can be many
                {
                    for (j = 0; j < count; j++)
                    {
                        string found = caseInsenList.ElementAt(j).Name.Trim(); // no spaces

                        if (field == found)
                            continue; // exact match, case sensitive, we already have this, skip
                        else
                        {

                        }
                    }

                }
            }

        }
    }


    public class AnimalHeader
    {
        public string Name { get; set; }
        public Type Type { get; set; }
        public int Order { get; set; }

    }

    public class AnimalHeaders : List<AnimalHeader>
    {

    }

Answer 1

Try a simple Linq: we are grouping same items and then add index spaces (underscopes) to each indexth item within a group. Finally, we flatten (combine) all groups.

  List<string> list = new List<string>() {
    "cat",      // the cat
    "Cat",      // first duplicate needs to become Cat_ (one space)
    "kitty",
    "kittY",
    "dog",
    "cAt",      // third duplicate needs to become cAt__ (two spaces)
    "Dog",
    "monkey",
    "monKey",
    "Monkey",
  };

  List<string> result = list
    .GroupBy(item => item, StringComparer.OrdinalIgnoreCase)
    .SelectMany(chunk => chunk
       .Select((item, index) => string.Format("{0}{1}", item, new string('_', index))))
    .ToList();

Demo:

Console.WriteLine(string.Join(Environment.NewLine, result));

Outcome:

cat
Cat_
cAt__
kitty
kittY_
dog
Dog_
monkey
monKey_
Monkey__

Edit: In case we want to preserve the initial order we have to store it (index of the item in the initial list) and finally order by it:

  List<string> result = list
    .Select((value, index) => new {
      value,
      index
    })
    .GroupBy(item => item.value, StringComparer.OrdinalIgnoreCase)
    .SelectMany(chunk => chunk
       .Select((item, index) => new {
          value = string.Format("{0}{1}", item.value, new string('_', index)),
          index = item.index
        }))
    .OrderBy(item => item.index)
    .Select(item => item.value)
    .ToList();

Outcome:

cat
Cat_
kitty
kittY_
dog
cAt__
Dog_
monkey
monKey_
Monkey__