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Pete O'Hanlon12-Sep-12 4:55
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QuestionRetrieve name of Printer using SendMessage Pin
toBeH_S11-Sep-12 22:10
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AnswerRe: Retrieve name of Printer using SendMessage Pin
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QuestionRandom Permutation Interface Pin
Skippums11-Sep-12 15:58
MemberSkippums11-Sep-12 15:58 
I would like to create an extension method that randomly permutes the contents of an ordered list (preferably in-place). This is what I have so far:

C#
public static class PermuteExtensions {

    public void Permute<T, U>(this T list) where T : IEnumerable<U> {
        // Create a copy of the input array
        U[] tempArray = list.ToArray();
        long arraySize = tempArray.LongLength;

        // Create a permutation of indexes, so list[j] = tempArray[indexes[j]]
        long[] indexes = new long[arraySize];
        // ...

        // Assign the new values to the existing ordered collection
        long j = 0;
        IEnumerator<U> enumer = list.GetEnumerator();
        while (enumer.GetNext()) {
            // Uh-oh, cannot assign to enumer.Current!
            enumer.Current = tempArray[indexes[j++]];
        }
    }

}
There are two problems with this approach:
1. I cannot figure out how to modify the contents of an IEnumerable object.
2. How to specify the constraint on T such that I allow this method to be called on the ordered collections (IList, Stack, Queue, List, LinkedList), but not on the unordered collections (IDictionary, Dictionary, ISet, Set).

It is NOT a firm requirement that this be an in-place algorithm. However, I don't know how to construct a new T object that offers a consistent way to add objects for all of the ordered collections listed above. Thanks,
Sounds like somebody's got a case of the Mondays

-Jeff

AnswerRe: Random Permutation Interface Pin
Dave Kreskowiak11-Sep-12 17:44
mveDave Kreskowiak11-Sep-12 17:44 
AnswerRe: Random Permutation Interface Pin
BillWoodruff12-Sep-12 0:05
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AnswerRe: Random Permutation Interface Pin
Pete O'Hanlon12-Sep-12 0:18
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Dave Kreskowiak12-Sep-12 2:21
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AnswerRe: Random Permutation Interface Pin
BobJanova12-Sep-12 1:17
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Pete O'Hanlon12-Sep-12 1:27
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Skippums12-Sep-12 6:41
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Questionconvert xdocument to integer Pin
rachel_m11-Sep-12 12:16
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AnswerRe: convert xdocument to integer Pin
Pete O'Hanlon11-Sep-12 12:22
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