Collection Like Dictionary That allows Value Change

Question

I understand why there isn't a method built in to do this, however I want a collection object that will allow Value change possibly during Enumeration.

Imagine the following:

Dictionary<string, List<string>> test =  new Dictionary<string, List<string>> {{"key", null}};

Lets say I have 20 of these within a class which implements IEnumberable

I'd like to use lambda or a simple foreach to iterate through the class and find the object matching a key, then store my List<T> with the Value parameter.

What's wrong with `if(test.ContainsKey("key"))test["key"] = myList;`? Why do you want to enumerate it? — Tim Schmelter, Oct 31 '12 at 15:54
Do you mean 20 dictionary-like objects, or 20 `string`/`List` pairs? If the latter, why do you want to iterate through the pairs rather than access the one you want directly by the key? — Rawling, Oct 31 '12 at 15:54
Thanks everyone, Tim I didn't think you'd be able to write it like, I was looking for a method of some description :). Time to look at writing the lookup part in lambda! — Ash G, Oct 31 '12 at 16:06

Christian Hayter · Answer 1 · 2012-11-02T13:54:21.380

0

You could avoid using an enumerator altogether, e.g.

var data = myEnumerable.ToArray();
for(var i = 0; i < data.Length; i++) {
    // here you can manipulate data[i] to your heart's content
}

edited Nov 02 '12 at 13:54

answered Oct 31 '12 at 15:57

Christian Hayter

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score 0 · Answer 2 · answered Oct 31 '12 at 16:11

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As you have discovered you can't change a DictionaryEntry through the Value property - you have to go through the Item accessor using the Key.

One option is to turn your Where results to an array then loop to get the matching Keys:

Dictionary<string, List<string>> test =  new Dictionary<string, List<string>>
                                             {{"key", null}};
test.Add("newKey",null);

var matches = test.Where(di => di.Key == "key").ToArray();

foreach(var di in matches) {
    test[di.Key] = new List<string> {"one","two"};

answered Oct 31 '12 at 16:11

D Stanley

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But why not just do `if (test.ContainsKey("key")) test["key"] = new List{...}`? – Rawling Oct 31 '12 at 16:14
@Rawling because the OP mentioned using a Lambda to find the matching keys. If it's just a simple string match then yes it could be simplified. – D Stanley Oct 31 '12 at 16:19
Eh, fair enough. It's a pretty confusing question. – Rawling Oct 31 '12 at 16:20

score 0 · Accepted Answer · edited May 23 '17 at 12:21

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You might be looking for a collection called multimap. See here for my implementation of it.

edited May 23 '17 at 12:21

Community

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answered Oct 31 '12 at 16:19

Olivier Jacot-Descombes

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score 0 · Answer 4 · answered Oct 31 '12 at 16:29

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You can just use this to modify a value in a dictionary:

public static void ChangeValue(string indexKey,List<string> newValue)
{
     if (test.ContainsKey(indexKey))
         keysDictionary[indexKey] = newValue;
}

answered Oct 31 '12 at 16:29

snorifu

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Collection Like Dictionary That allows Value Change

4 Answers4