Cannot use the output of LINQ query

Pavel

14y1.8kLINQ

Hello,

The initial task is to find all permutations of the byte array.
byte [] SFP = new byte[8] { 0, 1, 2, 3, 4, 5, 6, 7 };

I've found on some forum the following procedure:
public static IEnumerable<IEnumerable> Permute(IEnumerable list)

{if (list.Count() == 1)

return new List<IEnumerable> { list };

return list.Select((a, i1) => Permute(

list.Where((b, i2) => i2 != i1)).Select(

b => (

new List { a }).Union(b))

).SelectMany(c => c);

}

I use it in this way: var SFP_vars = Permute(SFP); It works fine - the query find all combinations.
The problem is that I can't use foreach to have access to particular memberes of list.
The foreach loop (see below) provoke the runtime error:
InvalidCastException was unhandled. Unable to cast object of type 'd__88`1[System.Byte]' to type 'System.Byte[]'

Construction, that give error:
foreach (byte[] SFP_var in SFP_vars)
{
}

How to circumvent the problem.

Thanks in advance.

Pavel.

6 Replies

Know the answer? Post it — somebody with the same question will find it here.

Vulpes14y ago
Accepted answer
OK, in that case, we can simplify it to this:

byte [] SFP = new byte[8] { 0, 1, 2, 3, 4, 5, 6, 7 };

var SFP_vars = Permute(SFP);

foreach (var SFP_var in SFP_vars)
{
SomeMethod(SFP_var.ToArray());
}
Pavel14y ago
The BEST !!! Works. Thanks Vulpes.
Pavel14y ago
Not exactly. Inside of foreach I call another function, where the value of a particular SFP_var is passed as parameter. In that another function the parameter, corresponding to SFP_var is declared as byte[].
Vulpes14y ago
Sure, if you're just interested in iteration, you could do this:

byte [] SFP = new byte[8] { 0, 1, 2, 3, 4, 5, 6, 7 };

var SFP_vars = Permute(SFP);

int count = 0;

foreach (var SFP_var in SFP_vars)
{
foreach(byte b in SFP_var) Console.Write("{0} ", b);
Console.WriteLine();
count++;
if (count == 20) break;
}

In practice, of course, you might not need the code to restrict iteration to 20 (or whatever) permutations if you're printing to a file or doing some other type of processing which doesn't involve printing to the console.
Pavel14y ago
Hi Vulpes, Your solution works. Thanks. Probaably my collection declaration (byte[]) isn't optimal - because it implies using additional loop (forming list). Is there some shorter solution ? Regards. Pavel.
Vulpes14y ago
Try this:

byte [] SFP = new byte[8] { 0, 1, 2, 3, 4, 5, 6, 7 };

var SFP_vars = Permute(SFP);

List list = new List();

foreach (var SFP_var in SFP_vars)
{
list.Add(SFP_var.ToArray());
}

// print out first 20, say

int count = 0;
foreach(byte[] ba in list)
{
foreach(byte b in ba) Console.Write("{0} ", b);
Console.WriteLine();
count++;
if (count == 20) break;
}