I have Dictionary from string key i want to get Value of corresponding key using Linq
Why do you want to get a value from a Dictionary using LINQ? You can just get the value using:
int value = dictionary[key];
You could use Single, but it's totally pointless and more code:
var keyValuePair = dictionary.Single(x => x.Key == key);
int value = keyValuePair.Value;
Why use Linq for something that is built in?
var val = myDict[key];
Use Linq where it makes sense (querying collections), not for something that is already well handled by the Dictionary classes.
returns the string value in this particular instance.
Disctionary<int, string> CustomValues = new Dictionary<int, string>();
CustomValues[int]; //CustomValues[key];
To Get the Value from the Dictionary Key
Dictionary<int,string>dict=new Dictionary<int,string>();
dict.Add(1,"Maha");
dict.Add(2,"Malathi");
dict.Add(3,"Mithra");
dict.Add(4,"Saravana");
var val=dict.Where(x=>x.Key==key).Select(x=>x.Value);//get the value from dictionary where key=3
(or)
var val=dict[Key];//get the value for Dictionary key 3.
Output: Mithra
Related
var listaFirme = new Dictionary<string, string>
{
{ "foo", "bar" }
};
var matchKey = "foo";
return listaFirme.Where(pair => pair.Key == matchKey).Select(pair => pair.Value).ToString();
I know that the keys are unique, so I want to return one value from my Dictionary. In this case it doesn't work, as it returns the string "System.IEnumerable<String>"...
It really does seem like you're overcomplicating this issue.
You can just use the indexer ([]) of the Dictionary class along with the .ContainsKey() method.
If you use something like this:
string value;
if (myDict.ContainsKey(key))
{
value = myDict[key];
}
else
{
Console.WriteLine("Key Not Present");
return;
}
You should achieve the effect that you want.
If you want to retrieve a value of a key from a dictionary access by indexer or TryGetValue:
var value = listaFirme[matchKey];
//If you don't know for sure that dictionary contains key
string value;
if(a.TryGetValue(matchKey, out value))
{
/* Code here */
}
As for why you got the result you did: Linq operations of Where and Select return an IEnumerable<T> so when doing ToString on it it executes the ToString of IEnumerable which is to print it's type.
Notice that listaFirme isn't a good name for a dictionary
If you did not have a dictionary and wanted to return one item then you'd use FirstOrDefault:
var value = someList.FirstOrDefault(item => /* some predicate */)?.Value;
It seems that you've overcomplicated the usage. In this case you don't need Linq.
Just use the Dictionary provided indexer: listaFirme[matchKey]. This returns the related value. IF the key does not exist the Dictionary throws a KeyNotFoundException exception. If you want to check if the key exists you can use the ContainsKey() method which returns a bool.
Replace toString(); with FirstOrDefault();
When you are applying .Where() condition it will return an Enumerable. You have to either cast it to list using .ToList() then you will get list of the values that meet the condition you used, or if you just want to get the first one you can use FirstOrDefault();
You can also write it like this
listaFirme.FirstOrDefault(pair => pair.Key == matchKey).Value
Since FirstOrDefault() accepts a predicate, you don't need always need to use .Where.
There is a SortedList
slLanguage = new SortedList();
slLanguage.Add("Bahasa","id-ID");
slLanguage.Add("Chinese Simplified(中文简体)","zh-CN");
slLanguage.Add("Chinese Traditional(中文繁體)","zh-TW");
slLanguage.Add("Kazakh","kk-KZ");
slLanguage.Add("Russian(русский)","ru-RU");
slLanguage.Add("Vietnamese(Việt)","vi-VN");
slLanguage.Add("English", "en-US");
How can I get the key by value?
For example: Get the item key "zh-CN"
If you would like to get the key from a value, you may use SortedList.IndexOfValue(object value) to get the index of the value you specify. Then, use SortedList.GetKey(int index) to return a key as object from the value's index we just gathered.
Example
SortedList slLanguage = new SortedList(); //Initializes a new SortedList of name slLanguage
//Add the keys and their values to the list
slLanguage.Add("Bahasa", "id-ID");
slLanguage.Add("Chinese Simplified(中文简体)", "zh-CN");
slLanguage.Add("Chinese Traditional(中文繁體)", "zh-TW");
slLanguage.Add("Kazakh", "kk-KZ");
slLanguage.Add("Russian(русский)", "ru-RU");
slLanguage.Add("Vietnamese(Việt)", "vi-VN");
slLanguage.Add("English", "en-US");
//
object returnedKey = slLanguage.GetKey(slLanguage.IndexOfValue("zh-CN")); //Gets the key from zh-CN as returnedKey of type object
Thanks,
I hope you find this helpful :)
There's probably a better way to do this, but here's one way to do it:
int index = slLanguage.IndexOfValue("zh-CN");
var item = slLanguage.GetKey(index);
Looking the key from Value would be not efficient and defeats the purpose of sorted List. Sorted list is really a sorted Dictionary named confusingly as SortedList.
I have an application that use managed dlls. One of those dlls return a generic dictionary:
Dictionary<string, int> MyDictionary;
The dictionary contains keys with upper and lower case.
On another side I am getting a list of potential keys (string) however I cannot guarantee the case. I am trying to get the value in the dictionary using the keys. But of course the following will fail since I have a case mismatch:
bool Success = MyDictionary.TryGetValue( MyIndex, out TheValue );
I was hoping the TryGetValue would have an ignore case flag like mentioned in the MSDN doc, but it seems this is not valid for generic dictionaries.
Is there a way to get the value of that dictionary ignoring the key case?
Is there a better workaround than creating a new copy of the dictionary with the proper StringComparer.OrdinalIgnoreCase parameter?
There's no way to specify a StringComparer at the point where you try to get a value. If you think about it, "foo".GetHashCode() and "FOO".GetHashCode() are totally different so there's no reasonable way you could implement a case-insensitive get on a case-sensitive hash map.
You can, however, create a case-insensitive dictionary in the first place using:-
var comparer = StringComparer.OrdinalIgnoreCase;
var caseInsensitiveDictionary = new Dictionary<string, int>(comparer);
Or create a new case-insensitive dictionary with the contents of an existing case-sensitive dictionary (if you're sure there are no case collisions):-
var oldDictionary = ...;
var comparer = StringComparer.OrdinalIgnoreCase;
var newDictionary = new Dictionary<string, int>(oldDictionary, comparer);
This new dictionary then uses the GetHashCode() implementation on StringComparer.OrdinalIgnoreCase so comparer.GetHashCode("foo") and comparer.GetHashcode("FOO") give you the same value.
Alternately, if there are only a few elements in the dictionary, and/or you only need to lookup once or twice, you can treat the original dictionary as an IEnumerable<KeyValuePair<TKey, TValue>> and just iterate over it:-
var myKey = ...;
var myDictionary = ...;
var comparer = StringComparer.OrdinalIgnoreCase;
var value = myDictionary.FirstOrDefault(x => String.Equals(x.Key, myKey, comparer)).Value;
Or if you prefer, without the LINQ:-
var myKey = ...;
var myDictionary = ...;
var comparer = StringComparer.OrdinalIgnoreCase;
int? value;
foreach (var element in myDictionary)
{
if (String.Equals(element.Key, myKey, comparer))
{
value = element.Value;
break;
}
}
This saves you the cost of creating a new data structure, but in return the cost of a lookup is O(n) instead of O(1).
For you LINQers out there that never use a regular dictionary constructor
myCollection.ToDictionary(x => x.PartNumber, x => x.PartDescription, StringComparer.OrdinalIgnoreCase)
There is much simpler way:
using System;
using System.Collections.Generic;
....
var caseInsensitiveDictionary = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
Its not very elegant but in case you cant change the creation of dictionary, and all you need is a dirty hack, how about this:
var item = MyDictionary.Where(x => x.Key.ToLower() == MyIndex.ToLower()).FirstOrDefault();
if (item != null)
{
TheValue = item.Value;
}
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.
Let's say you have a Dictionary called fooDictionary
fooDictionary.Values.ToList().IndexOf(someValue);
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.
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)
.FirstOrDefault();
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.
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;
}
}
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");
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
If searching for a value, you will have to loop through all the data. But to minimize code involved, you can use LINQ.
Example:
Given Dictionary defined as following:
Dictionary<Int32, String> dict;
You can use following code :
// Search for all keys with given value
Int32[] keys = dict.Where(kvp => kvp.Value.Equals("SomeValue")).Select(kvp => kvp.Key).ToArray();
// Search for first key with given value
Int32 key = dict.First(kvp => kvp.Value.Equals("SomeValue")).Key;
In your comment to max's answer, you say that what you really wanted to get is the key in, and not the index of, the KeyValuePair that contains a certain value. You could edit your question to make it more clear.
It is worth pointing out (EricM has touched upon this in his answer) that a value might appear more than once in the dictionary, in which case one would have to think which key he would like to get: e.g. the first that comes up, the last, all of them?
If you are sure that each key has a unique value, you could have another dictionary, with the values from the first acting as keys and the previous keys acting as values. Otherwise, this second dictionary idea (suggested by Jon Skeet) will not work, as you would again have to think which of all the possible keys to use as value in the new dictionary.
If you were asking about the index, though, EricM's answer would be OK. Then you could get the KeyValuePair in question by using:
yourDictionary.ElementAt(theIndexYouFound);
provided that you do not add/remove things in yourDictionary.
PS: I know it's been almost 7 years now, but what the heck. I thought it best to formulate my answer as addressing the OP, but of course by now one can say it is an answer for just about anyone else but the OP. Fully aware of that, thank you.
no , there is nothing similar IndexOf for Dictionary although you can make use of ContainsKey method to get whether a key belongs to dictionary or not
Dictionary<int, List<Customer>> dictionary = new Dictionary<int, List<Customer>>();
I want to query based on the key and get a List back. Not sure how to structure the LINQ query for that.
Desired Output:
A List<Customer> for a particular key in the Dictionary.
That's what the Dictionary (as you've defined the generic arguments) will do. So, dictionary[key] will return the list. Note that it will throw an exception if you haven't initialized it already with dictionary[key] = new List<Customer>();.
You don't need to use LINQ for this, but if you really want to
int key = 1;
List<Customer> customers = dictionary.Single(item => item.Key == key).Value;
The simplest way is to just retrieve the value for the key using the regular [] operator
dictionary[key];