arrays - Permutations of string collections in C#

Question

Seems like I'm stuck once again with recursive algorithms...

My application is supposed to sort files to different folders, according to the information specified by the user and according to a subfolder structure represented by a string like the following:

[ROOT]  brand  color  material  

The tags in the structure string represent collections:

Assume:

var brand = new List<string> { "Nike", "Adidas", "Reebok" };
var color = new List<string> { "red", "blue", "yellow", "black" };
var material = new List<string> { "leather", "fabric" };

var data = new List<List<string>>() { brand, color, material };

And what I 'm trying to get is something like:

[ROOT]Nike
edleather
[ROOT]Nike
edfabric
[ROOT]Nikelueleather
[ROOT]Nikeluefabric
[ROOT]Nikeyellowleather
[ROOT]Nikeyellowfabric
[ROOT]Nikelackleather
[ROOT]Nikelackfabric
[ROOT]Adidas
edleather
[ROOT]Adidas
edfabric
[ROOT]Adidaslueleather
[ROOT]Adidasluefabric
[ROOT]Adidasyellowleather
[ROOT]Adidasyellowfabric
[ROOT]Adidaslackleather
[ROOT]Adidaslackfabric
[ROOT]Reebok
edleather
[ROOT]Reebok
edfabric
[ROOT]Reeboklueleather
[ROOT]Reebokluefabric
[ROOT]Reebokyellowleather
[ROOT]Reebokyellowfabric
[ROOT]Reeboklackleather
[ROOT]Reeboklackfabric

The problem is that the amount of data tags (brand, color, material) and their order is not known in advance, hence the need for recursion.

Any idea?

Thank you so much in advance!

Answer 1

Here is the code By Eric Lippert. Cartesian Product..

http://ericlippert.com/2010/06/28/computing-a-cartesian-product-with-linq/

public static IEnumerable<IEnumerable<T>> CartesianProduct<T>(this IEnumerable<IEnumerable<T>> sequences)
{
    // base case: 
    IEnumerable<IEnumerable<T>> result = new[] { Enumerable.Empty<T>() };
    foreach (var sequence in sequences)
    {
        var s = sequence; // don't close over the loop variable 
        // recursive case: use SelectMany to build the new product out of the old one 
        result =
            from seq in result
            from item in s
            select seq.Concat(new[] { item });
    }
    return result;
}

---

var result = CartesianProduct(new List<List<string>>() {brand,color,material });

---

Usage Example:

var brand = new List<string> { "Nike", "Adidas", "Reebok" };
var color = new List<string> { "red", "blue", "yellow", "black" };
var material = new List<string> { "leather", "fabric" };

foreach (var row in CartesianProduct(new List<List<string>>() { brand, color, material }))
{
    Console.WriteLine(String.Join(",", row));
}