How to get continuous characters in C#?

Question

I've a

List<String> MyList=new List<string>();

I need to fill the list MyList with n values.

if the value of n is 2 then the list MyList will contain

"A","B"

if 10 then

"A","B","C"....."J"

if 30 then

"A"....."Z","AA","AB",AC","AD"

if 1000 then

"A",....."Z","AA","AB"......"AZ","BA","BB"......."BZ"........"YZ","AAA",AAB".....
and so on

I do not know how to do this.

Please help me to do this using any method Using LINQ or LAMBDA Expression

Answer 1

Edit 2:

This is probably the easiest way to implement it. I tested it, it works fine. You could generate a infinite number of strings.

public IEnumerable<string> GenerateStrings()
{
    foreach(string character in Alphabet())
    {
      yield return character;
    }

    foreach (string prefix in GenerateStrings())
    {
      foreach(string suffix in Alphabet())
      {
        yield return prefix + suffix;
      }
    }
}

public IEnumerable<string> Alphabet()
{
    for(int i = 0; i < 26; i++)
    {
      yield return ((char)('A' + i)).ToString();
    }
}

---

Stuff I wrote before:

You could also write a little recursive function which returns any string by a certain index. This may not be optimal performance wise, because there are some repetitive divisions, but it may be fast enough for your purpose.

It is quite short and easy:

string GetString(int index)
{
  if (index < 26)
  {
    return ((char)('A' + index)).ToString();
  }
  return GetString(index / 26 - 1) + GetString(index % 26);
}

usage (may also be put into another method:

List<string> strings = Enumerable.Range(0, 1000)
  .Select(x => GetString(x))
  .ToList();

This is working code, just wrote a test for it.

---

Edit: eg, the "full linq way" application of GetString:

public void IEnumerale<string> GenerateStrings()
{
  int index = 0;
  // generate "infinit" number of values ...
  while (true)
  {
     // ignoring index == int.MaxValue
     yield return GetString(index++);
  }
}

List<string> strings = GenerateStrings().Take(1000).ToList();

Answer 2

I did something similar in SQL a while back.

Translated to C# this is a function to create a code from a number:

public static string GetCode(int id) {
  string code, chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
  if (id <= chars.Length) {
    code = chars.Substring(id - 1, 1);
  } else {
    id--;
    int value = chars.Length, adder = 0;
    while (id >= value * (chars.Length + 1) + adder) {
      adder += value;
      value *= chars.Length;
    }
    code = chars.Substring((id - adder) / value - 1, 1);
    id = ((id - adder) % value);
    while (value > 1) {
      value /= chars.Length;
      code += chars.Substring(id / value, 1);
      id = id % value;
    }
  }
  return code;
}

Then you just get numbers from 1 and up, and translate into codes:

var codes = Enumerable.Range(1, 1000).Select(n => GetCode(n));

The limit of the function is currently "ZZZZZZ" or 321272406. (After that you get a division by zero.)

Note that this function uses all combinations and returns "A".."Z", "AA".."ZZ", "AAA"..."ZZZ" rather than starting at "AB" and "ABC".

Answer 3

This is similar to this question (but not quite enough to mark it as a duplicate, and it's a hard problem to search for anyway).

Use any of the working IEnumerable<string> answers (or at least, any which cover the range you need), and then if you need to create a list with a certain number of elements, just use:

List<string> list = GenerateSequence().Take(count).ToList();

Answer 4

This code is working fine, but I'm not sure if it's "LINQ enough".

char[] validChars = Enumerable.Range(0, 26).Select(i => (char)('A' + i)).ToArray();
List<string> result = new List<string>();
List<string> generator = validChars.Select(ch => ch.ToString()).ToList();

int n = 1000;

while (result.Count < n)
{
    result.AddRange(generator);
    generator = generator.Take((n - result.Count) / validChars.Length + 1)
                         .SelectMany(s => validChars.Select(ch => s + ch))
                         .ToList();
}

var output = result.Take(n);

Answer 5

Try the below .. I am using Cross Join and a Union to build the source and then filtering the record by using the Take extension method

char[] charArray = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();

List<String> MyList = new List<string>();
int n = 1000;

                      (from value1 in charArray
                       select new
                       {
                           newString = value1.ToString()
                       })
                   .Union
                   (
                       (from value1 in charArray
                        from value2 in charArray

                        select new
                        {
                            newString = string.Concat(value1, value2)
                        })
                    )
                    .Union
                    (
                        (from value1 in charArray
                         from value2 in charArray
                         from value3 in charArray

                         select new
                         {
                             newString = string.Concat(value1, value2, value3)
                         })
                     )
                     .Take(n)
                     .ToList()                         
                     .ForEach(i => MyList.Add(i.newString));

Hope this will give you some idea of using a combination of Linq,Lambda and Extension method.

Answer 6

@DannyChen this is it. your code with a little changes..

char[] validChars = Enumerable.Range(0, 26).Select(i => (char)('A' + i)).ToArray();

int n = 30;
int pointer = 0;
int pointerSec = 0;
int Deg = 0;
string prefix = string.Empty;
string prefixMore = string.Empty;
List<string> result = new List<string>();

while (n > 0)
{
    result.AddRange(validChars.Skip(pointer).Select(ch => prefix + ch).Take(n));
    if (pointer == 26)
    { 
        pointer = -1;
        Deg += 1;
        prefixMore = "" + validChars[pointerSec];
        pointerSec++;
        n++;
    }
    else
    {
        if (Deg == 0)
        {
            prefix = "" + validChars[pointer];
        }
        else
        {
            prefix = prefixMore + validChars[pointer];
        }
    }
    n--;
    pointer++;
}

it is 100% correct.