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);
Related
I have 2 data structures: Dictionary<string, string> and Multimap<string, string>.
Multimap is really just a Dictionary under the hood. I took must of the code from this question. Here's the class definition:
public class Multimap<TKey, TValue> : Dictionary<TKey, HashSet<TValue>>
{ ... }
Both data structures have a .Add(TKey key, TValue value) method.
I have a class that is responsible for populating these maps from certain files. I currently have the following two methods:
public Dictionary<string, string> PopulateDictionary(...)
{
Dictionary<string, string> returnDictionary = new Dictionary<string, string>();
...
foreach (...)
{
...
returnDictionary.Add(key, value);
}
return returnDictionary;
}
public Multimap<string, string> PopulateMultimap(...)
{
Multimap<string, string> returnMultimap = new Multimap<string, string>();
...
foreach (...)
{
...
returnMultimap.Add(key, value);
}
return returnMultimap;
}
As you can see, they're exactly the same, both around 25 lines long, and the only difference is their return type. What I am looking to do is condense this into one method.
My first attempt was to have the method
public Dictionary<string, object> PopulateGenericDictionary(...)
{ ... }
Where object was either string or HashSet<string>. But I didn't have much luck casting from Dictionary<string, object> to Multimap<string, string>.
Extracting the logic out of the methods is an option, but it's not great. Because of the foreach loops, there's always going to be some logic inside the two methods. You do end up with methods that are twice as small, but there's still two identical methods, which doesn't truly solve the problem.
This would be my ideal method structure:
public Dictionary<string, string> PopulateDictionary(...)
{
return MethodThatDoesAllTheLogic(...);
}
public Multimap<string, string> PopulateMultimap(...)
{
return MethodThatDoesAllTheLogic(...);
}
public ??? MethodThatDoesAllTheLogic(...)
{ ... }
I've been fiddling around with casting and generics, but I just can't get it to work. Any ideas?
Edit
I have used millimoose's solution. Here's my code now:
public Dictionary<string, string> GenerateDictionary(...)
{
Dictionary<string, string> returnMap = new Dictionary<string, string>();
PopulateDictionary(returnMap.Add, ...);
return returnMap;
}
public Multimap<string, string> GenerateMultimap(...)
{
Multimap<string, string> returnMap = new Multimap<string, string>();
PopulateDictionary(returnMap.Add, ...);
return returnMap;
}
private static void PopulateGenericDictionary(Action<string, string> addFunc, ...)
{
...
foreach (...)
{
addFunc(key, value);
}
}
Much cleaner!
To work around the lack of a common interface, you can invent one ad-hoc using a bunch of delegate type parameters:
void MethodThatDoesAllTheLogic(Action<string, string> addFunc)
{
// ...
addFunc(key, value);
// ...
}
public Dictionary<...> PopulateDictionary()
{
// ...
MethodThatDoesAllTheLogic(result.Add);
}
(Adding more parameters as necessary.)
I would avoid having the helper method create the actual collection at all; have it just populate an existing collection. That can be done much more effectively, since the Add method has the same signature in both cases. We can just use a delegate to accept the Add method:
public static void PopulateMapping<TKey, TValue>(Action<TKey, TValue> addMethod,
IEnumerable<TKey> data) //include other parameters needed to populate the data
{
foreach (var key in data)
{
addMethod(key, default(TValue));
}
}
Then it would be used like this:
public static Dictionary<string, string> PopulateDictionary()
{
Dictionary<string, string> output = new Dictionary<string, string>();
PopulateMapping<string, string>(output.Add, new string[] { "a" });
return output;
}
If you are only looking for an Add method, then both objects should share IDictionary. However, that Add method only uses objects. That is probably the closest that you can get without having to use generics in the method...but again you lose the benefits of generics at that point.
See if this approach will be useful:
The key is to make abstraction on creation of the object (Dictionary or Multimap) and aquiring the values - the two differences in the populating method.
public Dictionary<string, TValue> Populate<TValue>( Dictionary<string, TValue> returnDict, Func<SomeType, TValue> valueProvider)
{
string key = null;
...
foreach (...)
{
...
returnDict.Add(key, valueProvider(value));
}
return returnDict;
}
The example invocation is can be:
public void Test()
{
Populate(new Multimap<string, HashSet<string>>(), (t) => new HashSet<HashSet<string>>());
}
I'm not sure if the valueProvider delegate will be suited to your problem. Try to give more information about it.
If your inner logic is truly identical except for what type TValue is - and I mean word-for-word identical - then you could do something like:
IDictionary<string, TValue> MethodThatDoesAllTheLogic<TValue>(whatever)
{
// word for word-identical logic
}
I made the method take TValue as its only type parameter because that's the only difference (in the example you showed): both methods have string as the first type parameter.
ETA: This assumes that MultiMap implements IDictionary<K,V>. Since you said that it inherited from Dictionary<K,V> I assumed that it did.
in C# with generics you can require them to extend or implement a specific class in our case Dictionary, the following is how you might achieve that.
public T Populate<T>(string val) where T : Dictionary<string, string>, new()
{
T returnDict = new T();
returnDict.Add("key", "val");
return returnDict;
}
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Creating a constant Dictionary in C#
I currently have:
public string GetRefStat(int pk) {
return RefStat[pk];
}
private readonly Dictionary<int, int> RefStat =
new Dictionary<int, int>
{
{1,2},
{2,3},
{3,5}
};
This works but the only time I use the RefStat dictionary is when it is called by GetRefStat.
Is there a way I can combine the method and the dictionary?
Something like this?
public string GetRefStat(int pk)
{
return new Dictionary<int, int>
{
{1,2},
{2,3},
{3,5}
}[pk];
}
Yes, you can init the dictionary in the type's constructor. You can then change method GetRefStat to a property. So the meta code may look like this
class Foo
{
public Dictionary<int, int> RefStat {get;private set;}
Foo()
{
RefStat = new Dictionary<int, int>
{
{1,2},
{2,3},
{3,5}
};
}
}
And usage
Foo f = new Foo();
var item = f.RefStat[0]
Well you can make an extension method and then all dictionaries can use the function. I am going to assume that GetRefStat will be more than simply grabbing a value from a dictionary with a key:
public static class DictionaryExtensions
{
public static TValue GetRefStat<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, TKey key)
{
return dictionary[key];
}
}
Then all dictionaries can call it like:
var dictionary = new Dictionary<int, int>
{
{1,2},
{2,3},
{3,5}
};
var value = dictionary.GetRefStat(2)
If this dictionary is a bunch of constants then this answer is overkill. Just use if/else or switch.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Bidirectional 1 to 1 Dictionary in C#
Im curious if a datastructure exists in the standard .net libraries that can represent a 1-1 relationship, such as the following
1-a
4-b
6-c
5-d
Where I can say:
thisstructure[1] // returns "a"
thisstructure.GetKey["d"] // return 5
I understand all keys would have to be unique, does anything similar exist?
Thanks!
Yes- it's called KeyedCollection. It is intended to be subclassed and provides indexed access as well as access by a property derived from the added item. I usually make a generic subclass:
public class GenericKeyedCollection<TKey, TValue> : KeyedCollection<TKey, TValue> {
private readonly Func<TValue, TKey> _keyGenerator;
public GenericKeyedCollection(Func<TValue, TKey> keyGenerator) {
_keyGenerator = keyGenerator;
}
protected override int GetKeyForItem(TValue item)
{
return _keyGenerator(item);
}
}
To use it:
var myCollection = new GenericKeyedCollection<String, Car>(c=>c.Model);
myCollection.Add(new Car("Ford", "Mustang"));
var byIndex = myCollection[0];
var byModel = myCollection["Mustang"];
The only caveat is that the derived property (the "key") mustn't change after the item has been added.
If your key is not a property of the value, then you can use a Tuple<T1, T2> to combine the key and value:
var myCollection = new GenericKeyedCollection<String, Tuple<String, Car>>(t=>t.Item1);
myCollection.Add(new Tuple<String, Car>("Foo", Car("Ford", "Mustang")));
var byIndexCar = myCollection[0].Item2;
var byItem1Car = myCollection["Foo"].Item2;
Could this method fit your needs?
public static class Extensions
{
public static TKey GetKey<TKey, TValue>(this Dictionary<TKey, TValue> dict, TValue value)
{
int index = dict.Values.ToList().IndexOf(value);
if (index == -1)
{
return default(TKey); //or maybe throw an exception
}
return dict.Keys.ToList()[index];
}
}
You could then use it like so:
Dictionary<int, char> dict = new Dictionary<int, char>();
dict.Add(1, 'a');
dict.Add(4, 'b');
dict.Add(6, 'c');
dict.Add(5, 'd');
Console.WriteLine(dict.GetKey('d')); //5
The Dictionary....or IDictionary interface is the closest I can think of to what you want. It doesn't have quite so simple a searching operation, in that searching on a value can return the key, but I do know you can search on a key to get a value. providing functionality for the reverse in a custom extended class wouldn't be difficult at all.
MSDN IDictionary page
I'm trying to write an extension method to insert data into a dictionary of dictionaries defined as follows:
items=Dictionary<long,Dictionary<int,SomeType>>()
What I have so far is:
public static void LeafDictionaryAdd<TKEY1,TKEY2,TVALUE>(this IDictionary<TKEY1,IDictionary<TKEY2,TVALUE>> dict,TKEY1 key1,TKEY2 key2,TVALUE value)
{
var leafDictionary =
dict.ContainsKey(key1)
? dict[key1]
: (dict[key1] = new Dictionary<TKEY2, TVALUE>());
leafDictionary.Add(key2,value);
}
but the compiler doesn't like it. The statement:
items.LeafDictionaryAdd(longKey, intKey, someTypeValue);
gives me a type inference error.
For the statement:
items.LeafDictionaryAdd<long, int, SomeType>(longKey, intKey, someTypeValue);
I get "...does not contain a definition for... and the best extension method overload has some invalid arguments.
What am I doing wrong?
Some inventive generic usage ;-p
class SomeType { }
static void Main()
{
var items = new Dictionary<long, Dictionary<int, SomeType>>();
items.Add(12345, 123, new SomeType());
}
public static void Add<TOuterKey, TDictionary, TInnerKey, TValue>(
this IDictionary<TOuterKey,TDictionary> data,
TOuterKey outerKey, TInnerKey innerKey, TValue value)
where TDictionary : class, IDictionary<TInnerKey, TValue>, new()
{
TDictionary innerData;
if(!data.TryGetValue(outerKey, out innerData)) {
innerData = new TDictionary();
data.Add(outerKey, innerData);
}
innerData.Add(innerKey, value);
}
Try to use a concrete type:
public static void LeafDictionaryAdd<TKEY1,TKEY2,TVALUE>(this IDictionary<TKEY1, Dictionary<TKEY2,TVALUE>> dict,TKEY1 key1,TKEY2 key2,TVALUE value)
see the Dictionary<TKEY2,TVALUE> instead of IDictionary<TKEY2,TVALUE>
I'm guessing that this is a covariance / contravariance issue. Your method signature is expecting an IDictionary of IDcitionaries, but you're passing it an IDictionary of Dictionary. Try using a concrete Dictionary instead in your method signature, for the inner Dictionary.
If you specify an IDictionary on your Parameter list for the Extension method,
then your items will not match that.
Either change your Extension to
public static void LeafDictionaryAdd<TKEY1,TKEY2,TVALUE>(
this IDictionary<TKEY1, Dictionary<TKEY2,TVALUE>> dict,
TKEY1 key1,
TKEY2 key2,
TVALUE value)
OR Try and cast your items to
((IDictionary<long, IDictionary<int, YourType>>)items).LeafDictionaryAdd(l, i, o);
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);
}