I want to define a new member method for Dictionary as it already built in member methods e.g. Add(), Clear(), ContainsKey() etc.
That newly added member method should return all the keyvaluepairs in form of a Set as we can return map.entrySet() to Set in Java.
Can existing methods for dictionary be overridden to achieve this ?
You could create an extension method:
using System;
using System.Collections.Generic;
using System.Linq;
public static class DictionaryExtensions {
public static HashSet<KeyValuePair<TKey, TValue>> ToSet<TKey, TValue>(this Dictionary<TKey, TValue> dict) {
return new HashSet<KeyValuePair<TKey, TValue>>(dict.ToList());
}
}
Info about extension methods: https://msdn.microsoft.com/en-us/library/bb383977(v=vs.110).aspx
I'm aware it's not a set, but by using Linq you can get a list of key value pairs like so:
Dictionary<string, string> dictionary = new Dictionary<string, string>();
List<KeyValuePair<string, string>> keyValuePairs = dictionary.ToList();
Just in case it helps, you can access KeyValue pair of the Dictionary like this :
// Example dictionary
var dic = new Dictionary<int, string>{{1, "a"}};
foreach (var item in dic)
{
Console.WriteLine(string.Format("key : {0}, Value : {1}", item.Key, item.Value));
}
Related
This question already has answers here:
In C# 7 is it possible to deconstruct tuples as method arguments
(6 answers)
Closed 1 year ago.
Hi I have a function that returns a tuple of 2 values and I want to put them into a one-line add as seen below:
Dictionary<string, string> test = new Dictionary<string, string>();
test.Add(intoDict());
private (string, string) intoDict()
{
return ("Key","Value");
}
I need this to be a one-line operation.
If, for whatever reason it absolutely has to be a oneliner, you can create an extension method to handle the tuple value:
public static class Extension
{
public static void Add<TKey, TValue>(this IDictionary<TKey, TValue> dic, ValueTuple<TKey, TValue> tuple)
{
dic[tuple.Item1] = tuple.Item2;
}
}
which can then be called like this:
static (string, string) intoDict()
{
return ("Key", "Value");
}
static void Main(string[] args)
{
Dictionary<string, string> dic = new Dictionary<string, string>();
dic.Add(intoDict()); //added here
return;
}
You need to specify the key and value separately like below in Add method as it expects two parmeters, first key and second value :
var tupleResult = intoDict();
test.Add(tupleResult.Item1, tupleResult.Item2);
Consider using an extension method.
public static class DictionaryExtensions
{
public static void Add<T, U>(this IDictionary<T, U> Dictionary, (T, U) tuple)
{
Dictionary.TryAdd(tuple.Item1, tuple.Item2);
}
}
This extension method provides an .Add() to any IDictionary.
To use this simply do:
(string,string) myTuple = ( "Key", "Value");
dictionary.Add(myTuple);
My scenario,
how to convert List<KeyValuePair<string, string>> into IDictionary<string, string>?
Very, very simply with LINQ:
IDictionary<string, string> dictionary =
list.ToDictionary(pair => pair.Key, pair => pair.Value);
Note that this will fail if there are any duplicate keys - I assume that's okay?
Or you can use this extension method to simplify your code:
public static class Extensions
{
public static IDictionary<TKey, TValue> ToDictionary<TKey, TValue>(
this IEnumerable<KeyValuePair<TKey, TValue>> list)
{
return list.ToDictionary(x => x.Key, x => x.Value);
}
}
Use ToDictionary() extension method of the Enumerable class.
You can also use the constructor overload of Dictionary<TKey,TValue> that takes an IEnumerable<KeyValuePair<TKey,TValue>> as parameter.
var list = new List<KeyValuePair<int, string>>();
var dictionary = new Dictionary<int, string>(list);
I have the following List :
List<Dictionary<int, Dictionary<string, string>>> lngList
lngList.Add(new Dictionary<int,Dictionary<string,string>>().Add(1,new Dictionary<string,string>().Add("Item1Key","Item1Value")));
lngList.Add(new Dictionary<int,Dictionary<string,string>>().Add(3,new Dictionary<string,string>().Add("Item1Key","Item1Value")));
lngList.Add(new Dictionary<int,Dictionary<string,string>>().Add(2,new Dictionary<string,string>().Add("Item1Key","Item1Value")));
lngList.Add(new Dictionary<int,Dictionary<string,string>>().Add(4,new Dictionary<string,string>().Add("Item1Key","Item1Value")));
I need to sort (ascending) this list on the basis of the integer value present inside the Dictionary.
This has to be achieved without using LINQ.
P.S. This is assuming all the the integer values added are unique.
If each dictionary has only one key, and you don’t care what happens if it has multiple, you can do this:
lngList.Sort((a, b) => a.Keys.First().CompareTo(b.Keys.First()));
Since you stated that “This has to be achieved without using LINQ”, I assume you mean that the System.Linq namespace is not available to you. But that’s not a problem: you only need .First(), which you can easily define yourself:
public static class EnumerableExtensions {
public static T First<T>(this IEnumerable<T> source) {
using (var e = source.GetEnumerator()) {
if (!e.MoveNext())
throw new InvalidOperationException("The collection is empty.");
return e.Current;
}
}
}
If you have to use .NET 2.0, which doesn’t have lambda expressions or extension methods, use this instead:
lngList.Sort(new Comparison<Dictionary<int, Dictionary<string, string>>>(sortFunc));
public int sortFunc(Dictionary<int, Dictionary<string, string>> a,
Dictionary<int, Dictionary<string, string>> b)
{
return First(a.Keys).CompareTo(First(b.Keys));
}
public static T First<T>(IEnumerable<T> source) {
using (var e = source.GetEnumerator()) {
if (!e.MoveNext())
throw new InvalidOperationException("The collection is empty.");
return e.Current;
}
}
The easiest way to solve your solution is to use a SortedList instead of a List:
example:
SortedList<int, Dictionary<string, string>> lngList;
this will be sorted by default on the integer value
I need to add key/object pairs to a dictionary, but I of course need to first check if the key already exists otherwise I get a "key already exists in dictionary" error. The code below solves this but is clunky.
What is a more elegant way of doing this without making a string helper method like this?
using System;
using System.Collections.Generic;
namespace TestDictStringObject
{
class Program
{
static void Main(string[] args)
{
Dictionary<string, object> currentViews = new Dictionary<string, object>();
StringHelpers.SafeDictionaryAdd(currentViews, "Customers", "view1");
StringHelpers.SafeDictionaryAdd(currentViews, "Customers", "view2");
StringHelpers.SafeDictionaryAdd(currentViews, "Employees", "view1");
StringHelpers.SafeDictionaryAdd(currentViews, "Reports", "view1");
foreach (KeyValuePair<string, object> pair in currentViews)
{
Console.WriteLine("{0} {1}", pair.Key, pair.Value);
}
Console.ReadLine();
}
}
public static class StringHelpers
{
public static void SafeDictionaryAdd(Dictionary<string, object> dict, string key, object view)
{
if (!dict.ContainsKey(key))
{
dict.Add(key, view);
}
else
{
dict[key] = view;
}
}
}
}
Just use the indexer - it will overwrite if it's already there, but it doesn't have to be there first:
Dictionary<string, object> currentViews = new Dictionary<string, object>();
currentViews["Customers"] = "view1";
currentViews["Customers"] = "view2";
currentViews["Employees"] = "view1";
currentViews["Reports"] = "view1";
Basically use Add if the existence of the key indicates a bug (so you want it to throw) and the indexer otherwise. (It's a bit like the difference between casting and using as for reference conversions.)
If you're using C# 3 and you have a distinct set of keys, you can make this even neater:
var currentViews = new Dictionary<string, object>()
{
{ "Customers", "view2" },
{ "Employees", "view1" },
{ "Reports", "view1" },
};
That won't work in your case though, as collection initializers always use Add which will throw on the second Customers entry.
What's wrong with...
dict[key] = view;
It'll automatically add the key if it's non-existent.
simply
dict[key] = view;
From the MSDN documentation of Dictionary.Item
The value associated with the
specified key. If the specified key is
not found, a get operation throws a
KeyNotFoundException, and a set
operation creates a new element with
the specified key.
My emphasis
As usual John Skeet gets in there with lighting speed with the right answer, but interestingly you could also have written your SafeAdd as an Extension Method on IDictionary.
public static void SafeAdd(this IDictionary<K, T>. dict, K key, T value)...
Although using the indexer is clearly the right answer for your specific problem, another more general answer to the problem of adding additional functionality to an existing type would be to define an extension method.
Obviously this isn't a particularly useful example, but something to bear in mind for the next time you find a real need:
public static class DictionaryExtensions
{
public static void SafeAdd<TKey, TValue>(this Dictionary<TKey, TValue> dict,
TKey key, TValue value)
{
dict[key] = value;
}
}
I've got a Method that gets a IDictionary as a parameter.
Now I want to provide a method that retrieves the value from this dictionary, but it should be case-invariant.
So my solution to this right now was to have a static function that loops through the keys and converts them toLower() like this:
private static IDictionary<ILanguage, IDictionary<string, string>> ConvertKeysToLowerCase(
IDictionary<ILanguage, IDictionary<string, string>> dictionaries)
{
IDictionary<ILanguage, IDictionary<string, string>> resultingConvertedDictionaries
= new Dictionary<ILanguage, IDictionary<string, string>>();
foreach(ILanguage keyLanguage in dictionaries.Keys)
{
IDictionary<string, string> convertedDictionatry = new Dictionary<string, string>();
foreach(string key in dictionaries[keyLanguage].Keys)
{
convertedDictionatry.Add(key.ToLower(), dictionaries[keyLanguage][key]);
}
resultingConvertedDictionaries.Add(keyLanguage, convertedDictionatry);
}
return resultingConvertedDictionaries;
}
Now, this is ok, but still it's a pretty huge chunk of code that contradicts my idea of "clean and efficient". Do you know any alternatives to this so that the .ContainsKey() method of the dictionary doesn't differentiate between casing?
Yes - pass the Dictionary constructor StringComparer.OrdinalIgnoreCase (or another case-ignoring comparer, depending on your culture-sensitivity needs).
By using a StringDictionary the keys are converted to lower case at creating time.
http://simiansoftware.blogspot.com/2008/11/have-const-string-with-ui-description.html
You could use the var keyword to remove some clutter. Technically the source remains the same. Also I would just pass and return a Dictionary<string, string> because you're not doing anything with that ILanguage parameter and make the method more reusable:
private static IDictionary<string, string> ConvertKeysToLowerCase(
IDictionary<string, string> dictionaries)
{
var convertedDictionatry = new Dictionary<string, string>();
foreach(string key in dictionaries.Keys)
{
convertedDictionatry.Add(key.ToLower(), dictionaries[key]);
}
return convertedDictionatry;
}
... and call it like so:
// myLanguageDictionaries is of type IDictionary<ILanguage, IDictionary<string, string>>
foreach (var dictionary in myLanguageDictionaries.Keys)
{
myLanguageDictionaries[dictionary].Value =
ConvertKeysToLowerCase(myLanguageDictionaries[dictionary].Value);
}
You could inherit from IDictionary yourself, and simply marshal calls to an internal Dictionary instance.
Add(string key, string value) { dictionary.Add(key.ToLowerInvariant(), value) ; }
public string this[string key]
{
get { return dictionary[key.ToLowerInvariant()]; }
set { dictionary[key.ToLowerInvariant()] = value; }
}
// And so forth.
System.Collections.Specialized.StringDictionary() may help. MSDN states:
"The key is handled in a case-insensitive manner; it is translated to lowercase before it is used with the string dictionary.
In .NET Framework version 1.0, this class uses culture-sensitive string comparisons. However, in .NET Framework version 1.1 and later, this class uses CultureInfo.InvariantCulture when comparing strings. For more information about how culture affects comparisons and sorting, see Comparing and Sorting Data for a Specific Culture and Performing Culture-Insensitive String Operations."
You can also try this way
convertedDictionatry = convertedDictionatry .ToDictionary(k => k.Key.ToLower(), k => k.Value.ToLower());
LINQ version using the IEnumerable<T> extension methods:
private static IDictionary<ILanguage, IDictionary<string, string>> ConvertKeysToLowerCase(
IDictionary<ILanguage, IDictionary<string, string>> dictionaries)
{
return dictionaries.ToDictionary(
x => x.Key, v => CloneWithComparer(v.Value, StringComparer.OrdinalIgnoreCase));
}
static IDictionary<K, V> CloneWithComparer<K,V>(IDictionary<K, V> original, IEqualityComparer<K> comparer)
{
return original.ToDictionary(x => x.Key, x => x.Value, comparer);
}