Get the index of an element inside queue c#

Question

I have a queue of users(string of emails) a in c# and I want to send the user his location in this queue.

something like ;

Queue q = new Queue(32);

q.Enqueue(Session["email"].ToString());

    queue.IndexOf(email);

Any ideas?

thanks

Solution 1

Maybe a List or an Array would be better for such actions but you could try this:

queue.ToArray().ToList().IndexOf(email);

Solution 2

You can use extension method, something like:

public static int IndexOf<T>(this IEnumerable<T> collection, T searchItem)
{
    int index = 0;

    foreach (var item in collection)
    {
        if (EqualityComparer<T>.Default.Equals(item, searchItem))
        {
            return index;
        }

        index++;
    }

    return -1;
}

Solution 3

Queue is not the proper type to use IndexOf, look for List

Solution 4

Unfortunately, you cannot straightly use the plain old .NET Queue object. Queue is made for "blind" first-in-first-out logic, so that you cannot perform anything else but that.

If you really need to implement a queue in which you can find elements and retrieve their position (a very useful thing) try to wrap everything in a class that exposes the following methods:

public class CustomQueue<T> {
    private LinkedList<T> fifoList = new LinkedList<T>();

    public Enqueue(T newItem) {
        //add newItem at the head of fifoList
    }

    public T Dequeue() {
        //return and remove the item that is located at the tail of the queue
    }

    public int indexOf(T searchFor) {
        int ret = 0;
        for (T item: fifoList) {
            if (item.equals(searchFor)) return ret;
            ret++;
        }
    }
}

For better performance (queue and dequeue O(1) while indexOf O(n)) you should use a double-linked list

View more solutions

Comments

[baaroz]

no no I am using remote scripting to refresh the current location,every few mints

[baaroz]

I know there isn't IndexOf !It was just example of what I am trying to do

[Adrian Iftode]

This is an working solution, but it more an answer for the question: How to put a queue into a list so I can call the IndexOf method?

[Adrian Iftode]

What I mean is that if you need a collection for which you need to know the position of the element in that collection, then Queue is the wrong choice. @ionden answered how to do it, is the right way, but..

[mpen]

@baaroz: Well if you don't see something here, then there's really not much we can do for you. You need to choose a different container type. ionden is right. List<T>s can be used like queues anyway.

[ionden]

Indeed, but queue's don't offer an interface for returning the index so this is a compromise solution

[Adrian Iftode]

I'm ok with, but this needs a second thought, if possible

[usr-local-ΕΨΗΕΛΩΝ]

I agree with @AdrianIftode because while this all stands in a single line of code it takes a couple of O(n) operations. Not the most efficient, though effective

[baaroz]

this is nice solution ,I myself tought to use .ToArray to copy the queue and then iterates through the array with loop. but this is much more elegant

[AHAMED AAQIB]

Does Queue use zero-based index?

[flodis]

And not to forget the .ToList() returns a list of references to objects in the queue accessible for other purposes in the order added to the queue.