How to insert an item into a key/value pair object?

Question

Ok...here's a softball question...

I just need to be able to insert a key/value pair into an object at a specific position. I'm currently working with a Hashtable which, of course, doesn't allow for this functionality. What would be the best approach?

UPDATE: Also, I do need the ability to lookup by the key.

For example...oversimplified and pseudocoded but should convey the point

// existing Hashtable
myHashtable.Add("somekey1", "somevalue1");
myHashtable.Add("somekey2", "somevalue2");
myHashtable.Add("somekey3", "somevalue3");

// Some other object that will allow me to insert a new key/value pair.
// Assume that this object has been populated with the above key/value pairs.
oSomeObject.Insert("newfirstkey","newfirstvalue");

Thanks in advance.

Answer 1

Maybe the OrderedDictonary will help you out.

Answer 2

Hashtables are not inherently sorted, your best bet is to use another structure such as a SortedList or an ArrayList

Answer 3

I would use the Dictionary<TKey, TValue> (so long as each key is unique).

EDIT: Sorry, realised you wanted to add it to a specific position. My bad. You could use a SortedDictionary but this still won't let you insert.

Answer 4

Do you need to look up objects by the key? If not, consider using List<Tuple<string, string>> or List<KeyValuePair<string, string>> if you're not using .NET 4.

Answer 5

You could use an OrderedDictionary, but I would question why you would want to do that.

Answer 6

List<KeyValuePair<string, string>> kvpList = new List<KeyValuePair<string, string>>()
{
    new KeyValuePair<string, string>("Key1", "Value1"),
    new KeyValuePair<string, string>("Key2", "Value2"),
    new KeyValuePair<string, string>("Key3", "Value3"),
};

kvpList.Insert(0, new KeyValuePair<string, string>("New Key 1", "New Value 1"));

Using this code:

foreach (KeyValuePair<string, string> kvp in kvpList)
{
    Console.WriteLine(string.Format("Key: {0} Value: {1}", kvp.Key, kvp.Value);
}

the expected output should be:

Key: New Key 1 Value: New Value 1
Key: Key 1 Value: Value 1
Key: Key 2 Value: Value 2
Key: Key 3 Value: Value 3

The same will work with a KeyValuePair or whatever other type you want to use..

Edit -

To lookup by the key, you can do the following:

var result = stringList.Where(s => s == "Lookup");

You could do this with a KeyValuePair by doing the following:

var result = kvpList.Where (kvp => kvp.Value == "Lookup");

Last edit -

Made the answer specific to KeyValuePair rather than string.

Answer 7

Use a linked list. It was designed for this exact situation.
If you still need the dictionary O(1) lookups, use both a dictionary and a linked list.