更改字典键

Question

I am very new to dictionaries. Very new meaning that I started using them about 6 hours ago :p. Anyways, I want to know if there is a way to change the key of a dictionary.

Here is my dictionary:

Dictionary<string, string> Information = new Dictionary<string, string>();

Here is how I am adding to the dictionary (this is fired every time the user enters info and hits a button:

Information.Add(txtObjectNumber.Text, addressCombined);

The user needs to be able to edit both fields as well as remove the whole record.

So pretty much the application needs to add txtNumber and txtComments where txtNumber = txtObjectNumber

Thank you for your help.

Answer 1

It is not possible to directly modify a key. You'd have to remove it and re-add it.

Answer 2

The key is the mechanism that will allow you to find the data (the "value") later.

For example, if you did

information.Add("Kris", "Vandermotten");

you'd be able to find "Vandermotten" back later if you know "Kris".

Now in that context, what does it mean to change "Kris"? You put data in under the name "Kris" and want to get it back out searching for "Bob"? You won't find it.

In a way, dictionary key's are very much like primary keys in a relational database. The refer to the logical identity of the value. So for one thing, they should be uniquely identifying it.

So maybe this example doesn't make sense. Maybe something like

information.Add(42, new Person("Kris", "Vandermotten")

makes more sense. The question then of course is: what's the 42? Sometimes there is a natural candidate for such a key, like an employee number or something, sometimes there isn't.

When there is none, maybe you need to do

List<Person> information = new List<Person>();

information.Add(new Person("Kris", "Vandermotten"));

And of course, if a Person object allows changing the first name property, and that's what you want to do, then do it. But "changing dictionary keys" doesn't make a lot of sense to me.

Answer 3

You could use the built-in Remove() method for your Dictionary. Or you could do it the hard way by iterating through the collection. Although I'm curious as to why you would need to have to constantly update the keys, and not the values only.

Answer 4

You can't change the key of an existing dictionnary item. What you could do is delete the previous key and add a new key/value based on the edit.

Example use case:

Add Key:Name, Value: Bob

Now you want to change Name to FirstName , you would have to do

Remove key Name from dictionnary Add Key:FirstName, Value: Bob

Answer 5

Your use of a dictionary here seems a bit off. Like the name suggests, dictionaries are intended to provide you a way to "look up" a value, based on the key. In your case, though, you seem to be using it to store two related pieces of data, either of which can change. In that case, you're probably better off just using a list, and creating a separate class that encapsulates both pieces of information. Something like

public class MyData
{
    public string SomeData { get; set; }
    public string OtherData { get; set; }
}

and then

List<MyData> myDataList;

Or, you might even want to have a dictionary that maps a non-changing key (maybe a user id) to the custom class:

Dictionary<string, MyData> myDataDictionary;