Get index of a key/value pair in a C# dictionary based on the value

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I would like to know if some property or method exists that gets the index of a specific value.

I found that dictionaries have the Contains() method which returns true if the value passed in exists, so this method almost implements what I need.

I know that I can loop through all the value pairs and check the condition, but I ask because maybe there's an optimized way of doing this.

There's no such concept of an "index" within a dictionary - it's fundamentally unordered. Of course when you iterate over it you'll get the items in some order, but that order isn't guaranteed and can change over time (particularly if you add or remove entries).

Obviously you can get the key from a KeyValuePair just by using the Key property, so that will let you use the indexer of the dictionary:

var pair = ...;
var value = dictionary[pair.Key];
Assert.AreEqual(value, pair.Value);

You haven't really said what you're trying to do. If you're trying to find some key which corresponds to a particular value, you could use:

var key = dictionary.Where(pair => pair.Value == desiredValue)
                    .Select(pair => pair.Key)

key will be null if the entry doesn't exist.

This is assuming that the key type is a reference type... if it's a value type you'll need to do things slightly differently.

Of course, if you really want to look up values by key, you should consider using another dictionary which maps the other way round in addition to your existing dictionary.

Getting index of dictionary item based on item.key, Key); } public int GetIndex(OrderedDictionary<string, object> dictionary, string TValue> dictionary, TValue value) { int i = 0; foreach(var pair in  How to find a key in a Dictionary with C#. The ContainsKey method checks if a key already exists in the dictionary. The ContainsKey method checks if a key already exists in the dictionary. The following code snippet checks if a key already exits and if not, adds it. The ContainsValue method checks if a value already exists in the dictionary.

Let's say you have a Dictionary called fooDictionary


Values.ToList() converts your dictionary values into a List of someValue objects.

IndexOf(someValue) searches your new List looking for the someValue object in question and returns the Index which would match the index of the Key/Value pair in the dictionary.

This method does not care about the dictionary keys, it simply returns the index of the value that you are looking for.

This does not however account for the issue that there may be several matching "someValue" objects.

c#, Key; Label1.Text += " value: " + birds.ElementAt(i).Value; } //find index of dictionary elements by key. int index = birds.Keys.ToList().IndexOf(3); Label1.Text +=  Property Value. A TValue that is the value of the KeyValuePair<TKey,TValue>. Examples. The following code example shows how to enumerate the keys and values in a dictionary, using the KeyValuePair<TKey,TValue> structure. This code is part of a larger example provided for the Dictionary<TKey,TValue> class.

Consider using System.Collections.Specialized.OrderedDictionary, though it is not generic, or implement your own (example).

OrderedDictionary does not support IndexOf, but it's easy to implement:

public static class OrderedDictionaryExtensions
    public static int IndexOf(this OrderedDictionary dictionary, object value)
        for(int i = 0; i < dictionary.Count; ++i)
            if(dictionary[i] == value) return i;
        return -1;

c# - How to get key by index from a Dictionary, Net framework dictionary represents a collection of keys and values. each element of dictionary contain a key and value pair. so to get the dictionary key by index, first we Int32 which represents the zero based index of the element to retrieve. How to get key by index from a Dictionary; How to perform foreach loop through Dictionary keys; How to find a key by value in a Dictionary; How to get a key value pair from Dictionary; How to get first key value from Dictionary; How to add an item to a Dictionary if it does not exists; How to update a value in a Dictionary

    You can find index by key/values in dictionary
Dictionary<string, string> myDictionary = new Dictionary<string, string>();
myDictionary.Add("a", "x");
myDictionary.Add("b", "y");
int i = Array.IndexOf(myDictionary.Keys.ToArray(), "a");
int j = Array.IndexOf(myDictionary.Values.ToArray(), "y");

C#, Here, key is the Key which is to be located in the SortedList object. Return Value: This method returns the zero-based index of type System.Int32 of the key parameter So, the index of a specific key/value pair may change. This method uses a  A Dictionary stores Key-Value pairs where the key must be unique. Before adding a KeyValuePair into a dictionary, check that the key does not exist using the ContainsKey() method. Use the TryGetValue() method to get the value of a key to avoid possible runtime exceptions. Use a foreach or for loop to iterate a dictionary.

You can use LINQ to help you with this.

Dictionary<int, string> dict = new Dictionary<int, string>();
dict.Add(1, "hi");
dict.Add(2, "NotHi");
dict.Add(3, "Bah");

var item = (from d in dict
            where d.Value == "hi"
            select d.Key).FirstOrDefault();

Console.WriteLine(item); //Prints 1

Python, In this, first the dictionary is converted to a pair tuple and then the first element of Dictionary initialization with common dictionary · Python | Get key from value  C# program that uses ToString using System; using System.Collections.Generic; class Program { static void Main() { var pair = new KeyValuePair<string, int>("bird", 10); // Get string from KeyValuePair. string result = pair., I am wondering if I can get or extract the string name of the Key in a Dictionary. I have seen examples accessing the key from inside a foreach,  myList.First(kvp => kvp.Key == 5).Value Or if you want to use a dictionary (which might suit your needs better than the list as stated in the other answers) you convert your list to a dictionary easily: var dictionary = myList.ToDictionary(kvp => kvp.Key); var value = dictionary[5].Value;

get value of Dictionary keys via index number?, The C# Dictionary Add method takes two parameters, which mapping from a set of keys to a set of values. Each insertion to the Dictionary consists of a Key and its associated Value foreach (KeyValuePair item in myDictionary) { MessageBox. That means you get type safety with Dictionary, because you can't insert any  A Dictionary class is a data structure that represents a collection of keys and values pair of data. The key is identical in a key-value pair and it can have at most one value in the dictionary, but a value can be associated with many different keys. More about. C# Dictionary Dictionary Versus HashTable. Dictionary is a generic type, Hashtable is not.

What is the best way to iterate over a Dictionary in C#?, Parameters. key. The key to find in the dictionary. Return Value. The index for key and its associated value if key is in the dictionary; otherwise, nil . this method returns an index into the dictionary that corresponds with the key-value pair. With Remove, no remnants of the key-value pair are kept. Sometimes using null as a key's value is a better option—but this may add complexity to a program. Note: Running the code in Visual Studio, no exceptions are thrown. When we remove a key that doesn't exist, nothing happens.

  • Thanks, that is what i was looking for. I think i need to pull up my skills in LINQ. I read somewhere that LINQ is highly optimized, do you know if using that query is better than a foreach loop, check for every value and then return the key?
  • @voodoomsr: No, it would basically be doing a foreach loop within LINQ. How else could it do it, really?
  • +1 For OrderedDictionary, since Dictionary does not have indices.
  • I make a mistake in the question, i was referring to the key not the index, but what you respond here inspiring me to make other modifications, thanks.
  • Thank you for this code snippet, which might provide some limited short-term help. A proper explanation would greatly improve its long-term value by showing why this is a good solution to the problem, and would make it more useful to future readers with other, similar questions. Please edit your answer to add some explanation, including the assumptions you've made.