Shuffle characters of a string based on a key

Question

I have the following String:

String characters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";

I need to create two strings from it:

A string obtained simply by reordering the characters;
A string obtained by selecting 10 characters and reordering them.

So for (1) I would get, for example:

String characters = "jkDEF56789hisGHIbdefpqraXYZ1234txyzABCcglmnoRSTUVWuvwJKLMNOPQ0";

And for (2) I would get, for example:

String shortList = "8GisIbH9hd";

THE PROBLEM

I could just change to Char Array and order by randomly by a Guid.

However I want to specify some kind of key (maybe a guid?) and for that key the result or reordering and of selecting the shortList must be the same.

Does this make sense?

your problem is not clear. How can you "reorder" your first string "based on a Guid". I think you chose the wrong word. Could you explain what you really want step by step and what is your problem now? — artragis, Sep 21 '14 at 14:24
Are you looking to encode an arbitrary reordering of (1)62 and (2)10 characters in a Guid? You have 62 unique characters, so each could be represented by a 6 bit number. Thus an arbitrary reordering of 10 characters requires no more than 60 bits, and so could be encoded in a Guid (128 bits). An arbitrary reordering of all 62 characters requires more than 128 bits however, so your Guid would need to index into a table. — dbc, Sep 21 '14 at 15:02
Sorry, for the delay. I just updated my answer. Basically I want to reorder a string characters and selecting a portion of that string also reordered but the results would always be same according to a key ... So if I use as key "ksjdhkjhurer" then the results would only change if I change that key. — Miguel Moura, Sep 22 '14 at 17:01

score 0 · Answer 1 · edited May 23 '17 at 12:08

you could convert your GUID string to an int array of its ascii/utf/whatever codes like here Getting The ASCII Value of a character in a C# string. then iterate over this array with something along lines of this (note: this is pseudocode):

 string res="";
 for(elem in intconvertedGUIDstring) res+= characters[elem%(characters.count)];

for the task [2] you could reverse your Characters i.e. like here Best way to reverse a string and use the c# string function left() to truncate it before running it through the same procedure

brz · Answer 2 · 2014-09-22T20:46:13.130

You can use a hash function with a good distribution value as seed for comparison between elements. Here's a sample:

static ulong GetHash(char value, ulong seed)
{
   ulong hash = seed * 3074457345618258791ul;
   hash += value;
   hash *= 3074457345618258799ul;
   return hash;
}

And use this function for comparison:

static void Main()
{
   var seed = 53ul;
   var str = "ABCDEFHYUXASPOIMNJH";
   var shuffledStr = new string(str.OrderBy(x => GetHash(x, seed)).ToArray());
   Console.WriteLine(shuffledStr);
}

Now every time you order by seed 53 you'll get the same result, and if you seed by 54 you'll get a different result.

Shuffle characters of a string based on a key

2 Answers2