I have a bunch of classes that need to return properties as ReadOnlyCollection<T>s, which works well when they're just List<T>s, however, things get really sloppy with than list is inside a Dictionary<TKey, TValue>.
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For example, this is a typical List that I return as a ReadOnlyCollection:
private readonly List<string> _encryptionKeys;
public ReadOnlyCollection<string> EncryptionKeys => _encryptionKeys.AsReadOnly();
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However, this is the convulation I need to do for a ReadOnlyDictionary<TKey, TValue>:
private readonly ReadOnlyDictionary<string, ReadOnlyCollection<string>> _attributes;
public ReadOnlyDictionary<string, ReadOnlyCollection<string>> Attributes => _attributes;
... using a temporary variable:
Dictionary<string, List<string>> attributes = new Dictionary<string, List<string>>();
... to which I add values and its lists, I then build my property:
Dictionary<string, ReadOnlyCollection<string>> readonlyListDictionary = new Dictionary<string, ReadOnlyCollection<string>>();
foreach (string key in attributes.Keys)
readonlyListDictionary.Add(key, attributes[key].AsReadOnly());
_attributes = new ReadOnlyDictionary<string, ReadOnlyCollection<string>>(readonlyListDictionary);
================================================
Anyone have any suggestions?
Make it an extension method, then you don't have to think about it the whole time:
public static ReadOnlyDictionary<TKey, ReadOnlyCollection<TValue>> AsReadOnly<TKey, TValue>(this Dictionary<TKey, List<TValue>> source)
{
return new ReadOnlyDictionary<TKey, ReadOnlyCollection<TValue>>(
new Dictionary<TKey, ReadOnlyCollection<TValue>>(
source.Select(kvp =>
new KeyValuePair<TKey, ReadOnlyCollection<TValue>>(kvp.Key, kvp.Value.AsReadOnly())
));
}
Although, the constructor that takes IEnumerable<KeyValuePair> is only available in .NET 5. So in earlier versions we would have to foreach. This option may also be more performant as we pre-size the dictionary
public static ReadOnlyDictionary<TKey, ReadOnlyCollection<TValue>> AsReadOnly<TKey, TValue>(this Dictionary<TKey, List<TValue>> source)
{
var dict = new Dictionary<TKey, ReadOnlyCollection<TValue>>(source.Count);
foreach (var kvp in source)
dict[kvp.Key] = kvp.Value.AsReadOnly();
return new ReadOnlyDictionary<TKey, ReadOnlyCollection<TValue>>(dict);
}
Just use it like you use the other AsReadOnly extension.
Linq can do the heavylifting for you.
Dictionary<string, List<string>> input = new Dictionary<string, List<string>>();
ReadOnlyDictionary<string, ReadOnlyCollection<string>> output = new ReadOnlyDictionary<string, ReadOnlyCollection<string>>(dict.ToDictionary(kv => kv.Key, kv => kv.Value.AsReadOnly()));
Related
I have couple of methods and it keeps on expanding. So, I am planning to make it generic. Can anyone please help me with that. Atleast the method definition.
private static Dictionary<string, class1> PToDictionary(MapField<string, class1Proto> keyValuePairs)
{
Dictionary<string, class1> keyValues = new();
foreach (var pair in keyValuePairs)
{
**keyValues[pair.Key] = pToR(pair.Value);**
}
return keyValues;
}
My another method is :
private static Dictionary<Uri, class2> PToDictionary1(MapField<string, class2Proto> keyValuePairs)
{
Dictionary<string, class2> keyValues = new();
foreach (var pair in keyValuePairs)
{
**keyValues[new Uri(pair.Key)] = pToR1(pair.Value);**
}
return keyValues;
}
How can I make this generic so that when more methods are added, I dont need to add code.
I was thinking something like this, but errors are :
// Not sure how to call this method after Func is there
private static Dictionary<TKey, TValue> PToDictionary<TKey, TValue, TKeyProto, TValueProto>(MapField<TKeyProto, TValueProto> keyValuePairs, Func<TKeyProto, TKey> keyFunc, Func<TValueProto, TValue> valueFunc)
{
//How can I generalize my above method ?
}
Can someone help me complete the method ?
You don't need an extra method at all. LINQ already provides everything you need, combined with the fact that MapField implements IDictionary<TKey, TValue> (and therefore IEnumerable<KeyValuePair<TKey, TValue>>.
You'd just call:
var dictionary = repeatedField.ToDictionary(
pair => ConvertKey(pair.Key), pair => ConvertValue(pair.Value));
(where ConvertKey would be whatever code you want to convert the repeated field key into the dictionary key, and likewise for ConvertValue).
Sample calls:
var d1 = repeatedField1.ToDictionary(pair => pair.Key, pair => pToR(pair.Value));
var d2 = repeatedField2.ToDictionary(
pair => new Uri(pair.Key), pair => pToR1(pair.Value));
... but you may be able to remove the pToR and pToR1 methods anyway. (It's hard to tell without information about what they're doing...)
You can use the following method to convert MapField<TKeyProto, TValueProto> to Dictionary<TKey, TValue>:
public static Dictionary<TKey, TValue> PToDictionary<TKey, TValue, TKeyProto, TValueProto>(
MapField<TKeyProto, TValueProto> keyValuePairs,
Func<TKeyProto, TKey> mapKey,
Func<TValueProto, TValue> mapValue
)
{
Dictionary<TKey, TValue> keyValues = new();
foreach (var pair in keyValuePairs)
{
keyValues[mapKey(pair.Key)] = mapValue(pair.Value);
}
return keyValues;
}
Here, mapKey is a function that converts MapField's key to a dictionary key. Similarly, mapValue converts MapField's value to a dictionary value.
Another way is to make usage of LINQ ToDictionary extension method:
public static Dictionary<TKey, TValue> PToDictionary<TKey, TValue, TKeyProto, TValueProto>(
MapField<TKeyProto, TValueProto> keyValuePairs,
Func<TKeyProto, TKey> mapKey,
Func<TValueProto, TValue> mapValue
)
{
// this is possible because MapField<TKey, TValue> implements IEnumerable<KeyValuePair<TKey, TValue>>
return keyValuePairs.ToDictionary(
(KeyValuePair<TKeyProto, TValueProto> kvp) => mapKey(kvp.Key),
(KeyValuePair<TKeyProto, TValueProto> kvp) => mapValue(kvp.Value));
}
For example, if you want to convert MapField<string, string> to Dictionary<Uri, int> you can use the following code:
Dictionary<Uri, int> dictionary = PToDictionary(
map,
key => new Uri(key),
val => int.Parse(val));
Can anyone explain this problem?
Dictionary<string, List<string>> x
= new Dictionary<string, List<string>>();
IReadOnlyDictionary<string, IReadOnlyCollection<string>> y
= new Dictionary<string, IReadOnlyCollection<string>>();
y = x; // CS0266: Cannot implicitly convert type...
You can come close to what you're targeting like this:
Dictionary<string, List<string>> x = new Dictionary<string, List<string>>()
{
{ "Foo", new List<string> {"A", "B", "C"} }
};
IReadOnlyDictionary<string, ReadOnlyCollection<string>> y =
new ReadOnlyDictionary<string, ReadOnlyCollection<string>>(x.ToDictionary(k => k.Key, v => new ReadOnlyCollection<string>(v.Value)));
IReadOnlyCollection<string> foo = y["Foo"];
Note that ReadOnlyCollection<T> wraps your original list. It does not copy the elements. Same for the ReadOnlyDictionary<TKey, TValue>.
IReadOnlyDictionary is not covariant with respect to its value. This is to provide type safety around the TryGetValue method.
Consider this example:
Dictionary<string, List<string>> x = new Dictionary<string, List<string>>
{
{ "Key", new List<string>() }
};
IReadOnlyDictionary<string, IReadOnlyCollection<string>> y = new Dictionary<string, IReadOnlyCollection<string>>
{
{ "Key", new System.ArraySegment<string>() } //This is allowed because an ArraySegment implements IReadOnlyCollection<string>
};
List<string> foo;
x.TryGetValue("Key", out foo);
foo.Add("Some string");
The last three lines work for x because its value is a List<string>. It would not work if y were assigned to x because its value is not a List<string> and you can't call Add on it. This would not work:
y.TryGetValue("Key", out foo); //Error
Nor would this:
x = y;
x.TryGetValue("Key", out foo); //Error
Because it works for x and not for y, they are not type-compatible, so the cast is not allowed.
This Article perfectly describe the situation which you hit in your code.
Click 😀
Dictionary<TKey, TValue> is able to implement IReadOnlyDictionary<TKey, TValue>, because any code that takes the latter is promising not the modify the dictionary, which is a subset of the functionality the former provides.
But consider the other direction. You start with an IReadOnlyDictionary<TKey, TValue>, and you try to turn it into a regular Dictionary<TKey, TValue>. Now, you've taken something that had previously been promised to not be modified, and turned it into something that may be modified.
Clearly, that just won't do.
Furthermore, you can't just assume that the read-only implementation would throw an exception or something when modified (e.g. run-time safety even though not compile-time safety) because, as you know, you can always get the read-only interface from a mutable implementation.
So to be safe, you have two options:
Just copy the entire dictionary contents into a new object.
Wrap the read-only object in an IDictionary<TKey, TValue> implementation that does throw an exception if you try to modify it.
Note that the latter does not actually give you what you are specifically asking for. It's close, but it's not an actual instance of Dictionary<TKey, TValue>.
In terms of copying, you have many choices. Personally, I think ToDictionary() is itself just fine. But if you really don't like the verbosity, you can wrap it in an extension method:
public static Dictionary<TKey, TValue> ToDictionary<TKey, TValue>(
this IReadOnlyDictionary<TKey, TValue> dictionary)
{
return dictionary.ToDictionary(x => x.Key, y => y.Value);
}
I have the following method that makes a deep copy of a dictionary:
public static Dictionary<string, MyClass> deepCopyDic(Dictionary<string, MyClass> src)
{
//Copies a dictionary with all of its elements
//RETURN:
// = Dictionary copy
Dictionary<string, MyClass> dic = new Dictionary<string, MyClass>();
for (int i = 0; i < src.Count; i++)
{
dic.Add(src.ElementAt(i).Key, new MyClass(src.ElementAt(i).Value));
}
return dic;
}
I was wondering, can I somehow make it into a template? I need MyClass to be a template.
You can use Generics with where TValue : ICloneable constraint:
public static Dictionary<TKey, TValue> deepCopyDic<TKey, TValue>(Dictionary<TKey, TValue> src)
where TValue : ICloneable
{
//Copies a dictionary with all of its elements
//RETURN:
// = Dictionary copy
Dictionary<TKey, TValue> dic = new Dictionary<TKey, TValue>();
foreach (var item in src)
{
dic.Add(item.Key, (TValue)item.Value.Clone());
}
return dic;
}
You'll have to implement ICloneable interface in every class you'd like to pass into that method.
Or a bit improved version, with Key cloned as well:
public static Dictionary<TKey, TValue> deepCopyDic<TKey, TValue>(Dictionary<TKey, TValue> src)
where TValue : ICloneable
where TKey : ICloneable
{
return src.ToDictionary(i => (TKey)i.Key.Clone(), i => (TValue)i.Value.Clone());
}
You could use the copy constructor option:
Dictionary<string, int> copy = new Dictionary<string, int>(dictionary);
This way you make a deep copy of your dictionary.
Link to the original post.
The Serialized approach is the only way as noted above. ICloneable does not guarantee that all properties in the object being clone is not assigning references unless you have full control over the object which is never a good assumption, especially in a large team.
The only cavet of the Serialized approach is that all objects being passed in the dictionary are serializable. Also, serializing is not always very efficient because of the over use of Reflection that occurs, which shouldn't be used in high preformance areas of code.
I solved this problem using an approach known as fast serialization but it requires that all objects that you plan to clone support a specific interface. It's always speed vs. complexity.
Is there a method or technique that allows you to insert an element into a
Dictionary<TKey, TValue> guaranteeing that the item is in the first index of that dictionary's KeyCollection.
For example:
Dictionary<String, String> dic = foo.GetOutput();
// `dic` is something like:
// {"foo", "baa"},
// {"a", "b"}
I need something like:
dic.Add("key", "value", 0);
// where `0` is the index that `key` to be inserted.
foreach(KeyValuePair<String, String> key in dic)
{
Console.WriteLine("{0} = {1}", key.Key, key.Value);
}
Output:
key = value
foo = baa
a = b
By not using a dictionary.
Dictionary<TKey, TValue> is implemented as a hash-table. The position of keys internal to the dictionary depends upon the hash-code, the means by which that hash-code was reduced further to provide an index into its internal structure, and the order of insertion in an entirely implementation-dependant way.
This isn't the only way to implement a dictionary. SortedDictionary<TKey, TValue> uses a tree structure internally and so always keeps keys in an order. In this case we still can't insert something in the beginning, rather we insert something and it gets put in the appropriate place.
If ordering is what you care about most, then you don't want a puredictionary at all. Rather you want either a List<KeyValuePair<TKey, TValue>> or you want a structure that offers both the functionality of a list and of a dictionary, which is provided by OrderedDictionary. This isn't generic, but you can easily create a generic wrapper around it (doesn't give the performance benefits of internally using generics, but does give type-safety in use).
I know it is a three years old question. But found a workaround of this problem. It may help someone
Dictionary<String, String> dic = foo.GetOutput();
dic = (new Dictionary<string, string> {{"key","value"}}).Concat(dic).ToDictionary(k => k.Key, v => v.Value);
This will insert the element in the beginning of dictionary :)
Dictionaries are unordered; elements are meant to be retrieved with a key, whose hash points to its value's location.
What you might want is a List <KeyValuePair>, whose elements can be inserted into a specific index.
List<KeyValuePair<string, string>> list = dic.ToList();
list.Insert(0, new KeyValuePair<string, string>("a", "b"));
foreach(KeyValuePair<string, string> pair in list)
Console.WriteLine("{0} = {1}", pair.Key, pair.Value);
This is not possible with Dictionary<TKey, TValue> as it presents it's values in an unordered fashion when enumerated. There is SortedDictionary<TKey, TValue> which provides ordering but it does so by using an IComparer<TKey> against the key value directly. Here you want the key to be a String and have ordering based on an int. That is not possible with either of these types.
I think you'll need to implement a new type with these very specific semantics in them. For example.
class OrderedMap<TKey, TValue> {
private readonly Dictionary<TKey, TValue> _map = new Dictionary<TKey, TValue>();
private readonly List<TKey> _list = new List<TKey>();
public void Add(TKey key, TValue value) {
if (!_map.ContainsKey(key)) {
_list.Add(key);
}
_map[key] = value;
}
public void Add(TKey key, TValue value, int index) {
if (_map.ContainsKey(key)) {
_list.Remove(key);
}
_map[key] = value;
_list.Insert(index, key);
}
public TValue GetValue(TKey key) {
return _map[key];
}
public IEnumerabe<KeyValuePair<TKey, TValue>> GetItems() {
foreach (var key in _list) {
var value = _map[key];
yield return new KeyValuePair<TKey, TValue>(key, value);
}
}
}
Note this does come with some non-trivial performance differences over a traditional Dictionary<TKey, TValue>. For example Add and Remove are slower.
Dictionary<TKey, TValue> is inherently unordered (or rather, the ordering is unpredictable and shouldn't be relied upon). If you want some sort of ordering, you need to use a different type. It's hard to recommend any particular type without knowing more about your requirements.
The Dictionary<TKey, TValue> can't be ordered.
You can try SortedDictionary<TKey, TValue> instead, but that one is ordered by the Key, not by a separate index.
The Dictionary<TKey,TValue> class does not hold items in an ordered manner, so there is no "first" item.
There is a SortedDictionary<Tkey,TValue> (.NET 4.0+), which sorts by the key, but again, this is a very vague idea of "first".
this is my solution, maybe not the best solution but it works. =)
public static ComboBox FillDropDownList(Dictionary<String, String> dictionary, ComboBox dropDown, String selecione)
{
var d = new SortedDictionary<String, String>();
d.Add("0", selecione);
foreach (KeyValuePair<string, string> pair in dictionary)
{
d.Add(pair.Key, pair.Value);
}
dropDown.DataSource = new BindingSource(d, null);
dropDown.DisplayMember = "Value";
dropDown.ValueMember = "Key";
dropDown.SelectedIndex = 0;
return dropDown;
}
A Dictionary is an un-ordered collection. You could try OrderedDictionary - http://msdn.microsoft.com/en-us/library/system.collections.specialized.ordereddictionary.aspx - which has an Insert() method which is what you're after.
Is there streamlined way to convert list/enumberable of KeyValuePair<T, U> to Dictionary<T, U>?
Linq transformation, .ToDictionary() extension did not work.
.ToDictionary(kvp=>kvp.Key,kvp=>kvp.Value);
Isn't that much more work.
You can create your own extension method that would perform as you expect.
public static class KeyValuePairEnumerableExtensions
{
public static Dictionary<TKey, TValue> ToDictionary<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> source)
{
return source.ToDictionary(item => item.Key, item => item.Value);
}
}
This is the best I could produce:
public static IDictionary<TKey, TValue> ToDictionary<TKey, TValue>(IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs)
{
var dict = new Dictionary<TKey, TValue>();
var dictAsIDictionary = (IDictionary<TKey, TValue>) dict;
foreach (var property in keyValuePairs)
{
(dictAsIDictionary).Add(property);
}
return dict;
}
I compared the speed of converting an IEnumerable of 20 million key value pairs to a Dictionary using Linq.ToDictionary with the speed of this one. This one ran in 80% of the time of the Linq version. So it's faster, but not a lot. I think you'd really need to value that 20% saving to make it worth using.
Similar to the others, but using new instead of ToDictionary (since new already supports KeyValuePair enumerations) and allowing the passing of an IEqualityComparer<TKey>.
Also including a ToReadOnlyDictionary variant for completeness.
public static class EnumerableKeyValuePairExtensions {
public static Dictionary<TKey, TValue> ToDictionary<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IEqualityComparer<TKey>? comparer = null)
where TKey : notnull
=> new Dictionary<TKey, TValue>(keyValuePairs, comparer);
public static ReadOnlyDictionary<TKey, TValue> ToReadOnlyDictionary<TKey, TValue>(this IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs, IEqualityComparer<TKey>? comparer = null)
where TKey : notnull
=> new ReadOnlyDictionary<TKey, TValue>(keyValuePairs.ToDictionary(comparer));
}