Create a list from string list

Question

I need to create a List<string> with strings of 50 length; like this results:

...0000000000
...0000000001
...000000000z
...0000000010
...000000001z
...00000000zz
...0000000100
...00000001zz
...zzzzzzzzzz

My code is

ConcurrentBag<string> bags = new ConcurrentBag<string>();

string schar = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

for (int a1 = 0; a1 < schar.length; a1++)
{
    ...
    // 48 nested for loops here 
    ...
    for (int a50 = 0 ; a50 < schar.length ; a50++)
    {
        bags.add($"{schar[a1]}{schar[a2]}{schar[a3]}......to a50");
    }
}

In this case, I can use 50 nested for loops to create this list, but the code is very unreadable. Is there any method to create this? Thanks.

What's the logic behind the list entries? It's not immediately apparent from your example — Diado, Oct 02 '18 at 08:20
Possible duplicate of [Incrementing an alphanumeric string](https://stackoverflow.com/questions/26174022/incrementing-an-alphanumeric-string) — Drag and Drop, Oct 02 '18 at 08:27

Dmitry Bychenko · Accepted Answer · 2018-10-02T09:20:47.990

1

You can implement a simple generator:

private static IEnumerable<string> MyGenerator(
  int length, 
  string alphabeth = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz") {

  char[] item = Enumerable
    .Repeat(alphabeth[0], length)
    .ToArray();

  do {
    yield return new string(item);

    for (int i = item.Length - 1; i >= 0; --i) {
      int index = alphabeth.IndexOf(item[i]);

      if (index < alphabeth.Length - 1) {
        item[i] = alphabeth[index + 1];

        break;
      }

      item[i] = alphabeth[0];
    }
  }
  while (!item.All(c => c == alphabeth[0]));
}

Demo:

  var result = MyGenerator(3)
    .Take(100);

  string report = string.Join(Environment.NewLine, result);

  Console.Write(report);

Outcome:

In your case it can be something like this:

  var list = MyGenerator(50) // 50 characters in each item
    .Take(1000)              // take 1000 top items
    .ToList();               // materialize as a list

Please, note Take: the entire list (if not restricted) will be of

 62**50 == 4.16e89

items, which is a huge number.

edited Oct 02 '18 at 09:20

answered Oct 02 '18 at 08:28

Dmitry Bychenko

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thanks for `yield return`, this will not blow your RAM with 1.8938896e+79 terrabytes of strings – vasily.sib Oct 02 '18 at 08:32
@vasily.sib, at N e+79 e+12 byte, N=1 or 4 is not that big of a deal. There is 1.18e+57 atoms of hydrogen in the sun. Still 34 order of magnetude from that. It's so huge human brain min can easly be tricked by it. – Drag and Drop Oct 02 '18 at 09:00
@DragandDrop, I not sure what are you talking about:) all I mean is that as @kotodev is asking about getting all combinations of 50 symbol strings (`var list = MyGenerator(50).ToList();`) he must be prepared for a list of `62**50 (4.16e+89)` strings each of which is 50 bytes in length, so this is something about 1.89e+79 Tb of data. That's why `yield return` is extremly useful in this sample and that's why I upvote this answer. – vasily.sib Oct 02 '18 at 09:18
@vasily.sib, you corrected your math about Ram. My point was even if the original math was a bit wrong. It's so huge that it doesn't matter. e+79 Tb >>> to the number of atom of hydrogen in the sun. Thats how crazy the size is. If you consider that Tb is e+12byte. My aim was to to correct the math but to underline that you could have wrote 9,999, it would have hold the same value. It's an unrealistic amount of data. – Drag and Drop Oct 02 '18 at 09:29

Create a list from string list

1 Answers1