CODEWITHSUNDEEP
c#listdictionary
DebareDaDauntless
DebareDaDauntless

Reputation: 521

Dictionary and List

I want to use the dictionary in c# combined with a list like this

Dictionary<int, List<int>> Dir = new Dictionary<int, List<int>>();

but I am having trouble with the syntax for adding the keys and values. I thought if I just did something like

Dir.Add(integer1, integer2);

it would add integer1 was the key, and integer2 as the value. Then if I wanted to add to the integer1 key I would do

Dir.Add[interger1].Add(interger3);

I had one more question, I had a foreach loop like this to display the keys

 foreach (KeyValuePair<int, List<int>> k in labelsList)
 {
     Console.WriteLine(k.Key + " "+ k.Value);
 }

it displays the keys I expected up to 7, but it doesn't display the value's I wanted it to show, it just displays

1 System.Collections.Generic.List`1[System.Int32]

2 System.Collections.Generic.List`1[System.Int32]

3 System.Collections.Generic.List`1[System.Int32]

4 System.Collections.Generic.List`1[System.Int32]

5 System.Collections.Generic.List`1[System.Int32]

6 System.Collections.Generic.List`1[System.Int32]

7 System.Collections.Generic.List`1[System.Int32]

I have any idea to use a nested foreach like

foreach (KeyValuePair<int, List<int>> k in labelsList)
{
     foreach (KeyValuePair<int, List<int>> k in labelsList)
     {
         Console.WriteLine(k.Key + " " + k.Value);
     }
}

but I am unsure of what to put inside the nested foreach to iterate through the list

Upvotes: 1

Views: 366

Answers (5)

Fabian Bigler
Fabian Bigler

Reputation: 10895

If you want to add an item, simply use this code

(whereas dic is your Dictionary<Int32, List<Int32>>)

if (dic.ContainsKey(yourKey))
{
   dic[yourKey].Add(yourInt);
} else {
   dic[yourKey] = new List<int> { yourInt };
}

Upvotes: 0

Jan D&#246;rrenhaus
Jan D&#246;rrenhaus

Reputation: 6717

First, create an entry for your key integer1, unless you have already done so:

Dir.Add(integer1, new List<int>());

Then, find the right dictionary entry, then add to its value (in this case, your list):

Dir[integer1].Add(integer2);

You will find more entire code snippets in the other answers, if that is what you are looking for.

Upvotes: 0

jgauffin
jgauffin

Reputation: 101130

You have to add the collection into the dictionary before you can start adding values to it. Here is a solution which make one lookup (compared to two if ContainsKey is used). It also adds the list if it's missing.

public class YourClass
{
    private Dictionary<int, List<int>> _dictionary = new Dictionary<int, List<int>>();

    public void AddItem(int key, int value)
    {
        List<int> values;
        if (!_dictionary.TryGetValue(key, out values))
        {
            values = new List<int>();
            _dictionary.Add(key, values);
        }

        values.Add(value);
    }

    public IEnumerable<int> GetValues(int key)
    {
        List<int> values;
        if (!_dictionary.TryGetValue(key, out values))
        {
            return new int[0];
        }

        return values;
    }
}

Upvotes: 2

JeffRSon
JeffRSon

Reputation: 11166

You need to add a List<int> as value. It'll work like this:

if (!Dir.ContainsKey(integer1)) {
  Dir.Add(integer1, new List<int>());
}

var list = Dir[integer1];
list.Add(integer2);

Upvotes: 0

Joel Coehoorn
Joel Coehoorn

Reputation: 415600

When you call Dir.Add(), you need to provide a reference to a List<int> object. Providing an int itself is not right. So you need something like this:

Dir.Add(integer1, new List<int>());

Then you can update that entry like this:

Dir[integer1].Add(integer2);
Dir[integer1].Add(integer3);

Alternatively, you can use the collection initializer syntax:

Dir.Add(integer1, new List<int> { integer2, integer3});

Upvotes: 1

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