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);
Related
I'm trying to implement an extension method for all dictionaries whose value is of a type that implement a certain interface.
In this case I would like to have a ToListSortedByValue() method that returns
List<KeyValuePair<string, IComparable>>
for any dictionary of type
Dictionary<string, IComparable>
that would be cool because it would allow me to use dictionaries instead of lists, but to be able to have them sorted when needed (for example when printing in files or at console).
This is what I tried, but it doesn't work, any idea why?
public static List<KeyValuePair<string, IComparable>> ToListSortedByValue(this Dictionary<string, IComparable> Dic)
{
return Dic.OrderBy(x => x.Value).ToList();
}
EDIT:
it's solved already, but for completeness sake this is the problem I got:
when trying to use the method I got the an error as if such method didn't exist. If instead of IComparable I use an actual comparable type, let's say int or a class implementing IComparable, than it would work.
Basically you need to make the method generic on the value type and then constrain that type to be IComparable<T>.
public static List<KeyValuePair<string, T>> ToListSortedByValue<T>(
this Dictionary<string, T> Dic) where T : IComparable<T>
{
return Dic.OrderBy(x => x.Value).ToList();
}
This has the added bonus of returning the values as there passed in type. You might even want to make the key type generic too so it's not limited to just string
public static List<KeyValuePair<TKey, TValue>> ToListSortedByValue<TKey, TValue>(
this Dictionary<TKey, TValue> Dic) where TValue : IComparable<TValue>
{
return Dic.OrderBy(x => x.Value).ToList();
}
You need to make your method generic, so that it extends your actual type instead of just IComparable:
public static List<KeyValuePair<string, T>> ToListSortedByValue<T>(this Dictionary<string, T> Dic) where T : IComparable<T>
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));
}
I have a Dictionary which I want to filter by different conditions, e.g.
IDictionary<string, string> result = collection.Where(r => r.Value == null).ToDictionary(r => r.Key, r => r.Value);
I would like to pass the Where clause as a parameter to a method that performs the actual filtering, e.g.
private static IDictionary<T1, T2> Filter<T1, T2>(Func<IDictionary<T1, T2>, IDictionary<T1, T2>> exp, IDictionary<T1, T2> col)
{
return col.Where(exp).ToDictionary<T1, T2>(r => r.Key, r => r.Value);
}
This does not compile, though.
I have tried to call this method by using
Func<IDictionary<string, string>, IDictionary<string, string>> expression = r => r.Value == null;
var result = Filter<string, string>(expression, collection);
What am I doing wrong?
Where wants a Func<TSource, bool>, in your case Func<KeyValuePair<TKey, TValue>, bool>.
Furthermore, your return type of the method is incorrect. It should use T1 and T2 instead of string. Additionally, it is better to use descriptive names for the generic parameters. Instead of T1 and T2 I use the same names as the dictionary - TKey and TValue:
private static IDictionary<TKey, TValue> Filter<TKey, TValue>(
Func<KeyValuePair<TKey, TValue>, bool> exp, IDictionary<TKey, TValue> col)
{
return col.Where(exp).ToDictionary(r => r.Key, r => r.Value);
}
If you look at the constructor for the Where extension method you will see
Func<KeyValuePair<string, string>, bool>
So this is what you need to filter by, try this extension method.
public static class Extensions
{
public static IDictionairy<TKey, TValue> Filter<TKey, TValue>(this IDictionary<TKey, TValue> source, Func<KeyValuePair<TKey, TValue>, bool> filterDelegate)
{
return source.Where(filterDelegate).ToDictionary(x => x.Key, x => x.Value);
}
}
Call as
IDictionary<string, string> dictionairy = new Dictionary<string, string>();
var result = dictionairy.Filter((x => x.Key == "YourValue"));
I would like to create an extension method that will allow me to call ToSerializableDictionary(p => p.ID) instead of .ToDictionary(p => p.ID) in the following LINQ context. Though I'm not sure what class i'm supposed to be making an extension method for to replace ToDictionary<T>.
response.attributes = (
from granuleGroup in groups
let granuleRow = granuleGroup.First().First()
select new USDAttributes()
{
id = (int)granuleRow["id"],
...
attributes =
(
...
).ToDictionary(p => p.ID) <--** LINE IN QUESTION **
}
).ToList();
My SerializableDictionary class taken from here is so that I may serialize dictionary objects in my webservice to return hash tables that play nice with JSON.
Initially I was creating an extension method for IDictionary so I can do something like this: ...).ToDictionary(p => p.ID).ToSerializableDictionary(); But this has been a complete failure because it's my first time creating extension methods and I don't know what I'm doing.
public static class CollectionExtensions
{
public static SerializableDictionary<string, object> ToSerializableDictionary(this IDictionary<string,object> sequence)
{
SerializableDictionary<string, object> sDic = new SerializableDictionary<string, object>();
foreach (var item in sequence)
{
}
return sDic;
}
}
public static SerializableDictionary<TKey, T> ToSerializableDictionary<TKey, T>(this IEnumerable<T> seq, Func<T, TKey> keySelector)
{
var dict = new SerializableDictionary<TKey, T>();
foreach(T item in seq)
{
TKey key = keySelector(item);
dict.Add(key, item);
}
return dict;
}
Actually the class you provided has a handy constructor for doing this, so you can actually do
attributes = new SerializableDictionary( (
...
).ToDictionary(p => p.ID) );
But here you go with the extension method (again using that constructor):
public static partial class Extension {
public static SerializableDictionary<T, Q> ToSerializableDictionary(
this IDictionary<T, Q> d) {
return new SerializableDictionary(d);
}
}
Lee's response is the correct answer but just to offer another approach you could try this slightly terser version:
public static SerializableDictionary<TKey, T> ToSerializableDictionary<TKey, T>(this IEnumerable<T> seq, Func<T, TKey> keySelector)
{
var dict = seq.ToDictionary(keySelector);
//since SerializableDictionary can accept an IDictionary
return new SerializableDictionary<TKey, T>(dict);
}
Personally however I'd consider an even simpler approach and use JSON.Net for this task - it works perfectly, is ridiculously simple to use and is incredibly fast. I believe Microsoft have even switched to using JSON.Net in MVC3 (or perhaps 4?) for these reasons. Heartily recommended
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);
}