I have an interesting problem. I need to write a general (I'd use the word "generic" but that would conflict with what I'm after) routine that I can hand an instance of a dictionary object instance and iterate over the content of said object as a dictionary and return the content as literal values. The difficulty lies in that the method parameter will be of type "object", not dictionary.
What I need now and can't figure out how to do, is a way of iterating over a Dictionary<K, V> of arbitrary keys and values. Easy to do if you know the types going in, but as I say, the origin of the dictionary will be as an object where object.GetType().GetInterfaces() has typeof(IDictionary) in the results. I won't know (and shouldn't need to know) the dictionary key type or the value type.
My current need is to process something that is Dictionary<string, SomeClass>;. Once I get the list of keys I can use a foreach on each instance, figure out that it's a string and proceed from there. With the Values it'll be an instance of some class (the class will change but again, I can pass that off to another set of methods to extract the class, extract the properties of the class and extract those values).
The main point of the request is to obtain a method (or two or however many) that will allow me to iterate over a dictionary of unknown types and extract the keys and values, all without knowing the types at compile time. The above Dictionary; is just an example, I need to be able to pass any dictionary. At the moment, I'm not worried about edge cases like Dictionary<Tuple<int, string, SomeOtherClass>, SomeClass>> or things like that, if I can start with Dictionary<string, SomeClass>;, I can probably proceed from there.
It's getting the keys and values out in a form that I can process that I haven't figured out how to do yet.
You mentioned that you have access to the IDictionary<K,V> interface on the object. You can then use get_Keys and get_Values to access the keys and values respectively.
Also, IDictionary<K,V> derives from IEnumerable<KeyValuePair<K,V>> so you can also access the list of key-value pairs using a for-loop similar to lists.
EDIT - Clarification:
IDictionary inputAsDictionary = input as IDictionary;
if (inputAsDictionary != null)
{
// Valid : input is a dictionary.
ICollection dictKeys = inputAsDictionary.Keys; // This is a list of all keys
ICollection dictValues = inputAsDictionary.Values; // This is a list of all values
// Iterate over all keys
for(var dictKey in dictKeys)
{
Console.WriteLine(dictKey); // Print the key
Type dictKeyType = dictKey.GetType(); // Get the type of key if required
// ...
}
// Similarly, iterate over all values
for(var dictValue in dictValues)
{
Console.WriteLine(dictValue); // Print the value
Type dictValueType = dictValue.GetType(); // Get the type of value if required
// ...
}
}
You can also do this using the generic Dictionary<K,V> interface, but it gets a lot more complicated to get the types. You will need to call Type.GenericTypeArguments and go from there. The example I have shown seems simpler.
Related
I am wondering about whether or not creating a list of an anonymous type is the best way to effectively create a list of multiple types as well as its effect on general performance and efficiency. Mainly I just want to know if there is a more standard way of doing List?
Situation
I every now and then find myself with a need to create a list that has multiple values each of a different type, List. Normally i would just resolve this with a Dictionary, but then there are the cases where i don't care about duplicated key values or need a 3rd (or rarely 4th) value. Usually this is for temporary list that just track something contained in a method like logging thrown errors and an associated value so that at the end of the method i can string together the messages for a log file or something.
What i have so far is this:
var list = new[] { new { RowNumber = 1, Message = "" } }.ToList();
list.Clear();//clears out the example used to create the anonymous type
list.Add(new { RowNumber = 10, Message = "bla bla" }); //adding to the list
I am debating on doing something like an extension or something to make this easier, but if the performance sucks or there is a better way, i would like to know.
I prefer to make a class. The IL just makes an anonymous class in native that gets called the same way as a normal class, so there is no performance hit associated with it. If you ever debug anonymous types, you'll notice the name has a long name like AnonymousTypes.Program+f__1
Creating a class improves the readability of your code IMO.
public class RowMessage
{
public int RowNumber { get; set; }
public string Message { get; set; }
}
You can also use Tuples, but even this is still unclear:
public void MyMethod()
{
Tuple<int, string> myTuple = new Tuple<int, string>(1, "hi");
List<Tuple<int, string>> myTupList = new List<Tuple<int, string>>();
myTupList.Add(myTuple);
}
I just experimented a little. Here's what I found:
Anonymous types are as good as anything else. I can't really say "anything," since I didn't try everything. But I can tell you that they're as good as Tuple<> and concrete types. This is logical, because underneath the covers, the compiler actually builds types for anonymous types. In essence, at runtime, they are just concrete types.
Your ToList call is redundant. This part's important. It's not super relevant to your immediate question, but looking at your example, you do new [] { ... }.ToList(). This forces a loop through the array after it's created. You'd be much better off using list initialization: new List<dynamic> { ... };. That's what I used in my examples.
I ran tests 10,000 times each for:
Anonymous type with array initializer (00:00:00.0050338 total)
Anonymous type with list initializer (00:00:00.0035599 total)
Tuple with list initializer (00:00:00.0025857 total)
Concrete type with list initializer (00:00:00.0041538 total)
Running them again would just mix it up. The only consistent result was that arrays were, unsurprisingly, slower than going directly to a list.
If you're going to make an extension method, you'll probably want to go with one of the latter two options. Anonymous types don't travel well outside of their scope, as I'm sure you know. The choice is yours between concrete types and tuples. I'd go with concrete if you're using it a lot and/or outside of the original method, and a tuple if it just needs to exist somewhere. That's really a design choice that I can't make for you.
Since you are talking about enriching Exceptioninformation it is worth to mention that the Exceptionclass implements a property called Data which is of type IDictionary and can be used to append additional information.
try
{
throw new FileNotFoundException{ Data ={ { "TEST", "Hello World" } } };
}
catch (Exception e)
{
Console.WriteLine(e.Data["TEST"]);
...
e.Data.Add("Whatever", DateTime.Now);
}
If you find yourself adding the same information lots of times, consider some HelperMethods that add certain information to a giving exception. This could also take care for duplicated keys which use some sort of numeric postfix that increments like fileName_1 and so on, you get the idea.
You can also create a standartized method of outputting those Information you provided yourself.
If you want a more Complex approach you can just simply use List but make the consumer of this list handle each kind of type. Which is basically the idea behind the DebuggerTypeProxy-Atrribute
So you can for example use some pattern like this:
foreach(var typeGroup in additionalInformation.GroupBy(item => item.GetType())
{
ITypedLogHandler handler = GetHandlerFor(typeGroup.Key);
handler.WriteLog(typeGroup);
}
In general the only reason I can think of this whole idea to beeing valid is some convenient debuggint/loggin approach. Anything else should really use strong typing.
I have a class with a bunch of methods in it, the methods transfer variables elsewhere in my program when called. I want to use a dictionary as the middle man between the methods that transfer data and the methods that call them.
So here is my question. Say I make a dictionary, where the key is an int and I want the value to be the name of a method. I will assign a new value / method each time I add to the dictionary. Is there a value type I can put there that will let me do this?
Dictionary<int, ?> methodKey= new Dictionary<int, ?>();
I tried to find a list of types that dictionary will take but I couldn't find anything specific.
Thanks in advance
Use any delegate type as a type of value. For example:
Dictionary<int, Action>
So, you'll be able to write such things:
dictionary[0] = () => Console.WriteLine("0");
dictionary[1] = Foo;
dictionary[2] = a.Bar;
Specific delegate type depends on your needs - may be, you want for methods to have some input parameters or output/return values, but it should be most common type.
Will all the methods have the same signature? If so you can probably use one of the existing Action or Func delegate, (or you can create a delegate type with that signature), and use that as your second type parameter.
If not, you can use Delegate (or even object) and cast to the appropriate type when you invoke the delegates.
So I have:
ConcurrentDictionary<string, int> dict;
I want to pass a reference to one of its elements, suppose dict["x"] to a method, and allow that method to change/set that element. Is it possible to do exactly that, or do I have to pass the dictionary itself? Also, is it possible to do so even if the element does not exist as a key in the dictionary? Or does it already has to be a valid key contained in the dictionary?
Yes, by using a delegate. This delegate can be called from within the changing function. The delegate will then change or set the key/value inside the dictionary.
void DoChangeMyElement<T>(Action<T> changeIt)
{
changeIt(123);
}
You can call this method with:
ConcurrentDictionary<string, int> dict = new ...;
DoChangeMyElement(value => dict["X"] = value);
I want to pass a reference to one of its elements, suppose dict["x"] to a method, and allow that method to change/set that element. Is it possible to do exactly that, or I have to pass the dictionary itself ?
Just pass the dictionary, as Sam I am said it is a reference type anyway.
Also, is it possible to do so even if the element does not exist as a key in the dictionary ?
No that's not possible, you'd have to add to it, then send it to the function.
You'd have to pass the whole dictionary and key, and let the method do what it needs to. The basic reason for this is that you can only pass fields and local variables by reference, not properties (including indexer properties).
If you were really desperate to do so, you could use reflection and/or delegates to get what you want done, but it's not the best way to do it.
There's no harm in passing the whole Dictionary. It itself is a reference type after all, and passing the Dictionary would be better form than passing by reference.
but I suppose you could encapsulate you int and pass it like that
public class IntContainer
{
int value;
}
I wanted to add a KeyValuePair<T,U> to a Dictionary<T, U> and I couldn't. I have to pass the key and the value separately, which must mean the Add method has to create a new KeyValuePair object to insert, which can't be very efficient. I can't believe there isn't an Add(KeyValuePair<T, U>) overload on the Add method. Can anyone suggest a possible reason for this apparent oversight?
You can use the IDictionary<TKey,TValue> interface which provides the Add(KeyValuePair<TKey,TValue>) method:
IDictionary<int, string> dictionary = new Dictionary<int, string>();
dictionary.Add(new KeyValuePair<int,string>(0,"0"));
dictionary.Add(new KeyValuePair<int,string>(1,"1"));
Backup a minute...before going down the road of the oversight, you should establish whether creating a new KeyValuePair is really so inefficient.
First off, the Dictionary class is not internally implemented as a set of key/value pairs, but as a bunch of arrays. That aside, let's assume it was just a set of KeyValuePairs and look at efficiency.
The first thing to notice is that KeyValuePair is a structure. The real implication of that is that it has to be copied from the stack to the heap in order to be passed as a method parameter. When the KeyValuePair is added to the dictionary, it would have to be copied a second time to ensure value type semantics.
In order to pass the Key and Value as parameters, each parameter may be either a value type or a reference type. If they are value types, the performance will be very similar to the KeyValuePair route. If they are reference types, this can actually be a faster implementation since only the address needs to be passed around and very little copying has to be done. In both the best case and worst case, this option is marginally better than the KeyValuePair option due to the increased overhead of the KeyValuePair struct itself.
There is such a method – ICollection<KeyValuePair<K, T>>.Add but as it is explicitly implemented you need to cast your dictionary object to that interface to access it.
((ICollection<KeyValuePair<KeyType, ValueType>>)myDict).Add(myPair);
See
List of Explicit Interface Implementations on Dictionary<K, T>'s documentation page (you'll need to scroll down).
Explicit member implementation
The page on this method includes an example.
Should somebody really want to do this, here is an Extension
public static void Add<T, U>(this IDictionary<T, U> dic, KeyValuePair<T, U> KVP)
{
dic.Add(KVP.Key, KVP.Value);
}
but i would recommend to not do this if there is no real need to do this
Unless I'm mistaken, .NET 4.5 and 4.6 adds the ability to add a KeyValuePair to a Dictionary. (If I'm wrong, just notify me and I'll delete this answer.)
https://msdn.microsoft.com/en-us/library/cc673027%28v=vs.110%29.aspx
From the above link, the relevant piece of information is this code example:
public static void Main()
{
// Create a new dictionary of strings, with string keys, and
// access it through the generic ICollection interface. The
// generic ICollection interface views the dictionary as a
// collection of KeyValuePair objects with the same type
// arguments as the dictionary.
//
ICollection<KeyValuePair<String, String>> openWith =
new Dictionary<String, String>();
// Add some elements to the dictionary. When elements are
// added through the ICollection<T> interface, the keys
// and values must be wrapped in KeyValuePair objects.
//
openWith.Add(new KeyValuePair<String,String>("txt", "notepad.exe"));
openWith.Add(new KeyValuePair<String,String>("bmp", "paint.exe"));
openWith.Add(new KeyValuePair<String,String>("dib", "paint.exe"));
openWith.Add(new KeyValuePair<String,String>("rtf", "wordpad.exe"));
...
}
As can be seen, a new object of type Dictionary is created and called openWith. Then a new KVP object is created and added to openWith using the .Add method.
just because the enumerator for the Dictionary class returns a KeyValuePair, does not mean that is how it is implemented internally.
use IDictionary if you really need to pass KVP's because you've already got them in that format. otherwise use assignment or just use the Add method.
What would be wrong with just adding it into your project as an extension?
namespace System.Collection.Generic
{
public static class DictionaryExtensions
{
public static void AddKeyValuePair<K,V>(this IDictionary<K, V> me, KeyValuePair<K, V> other)
{
me.Add(other.Key, other.Value);
}
}
}
I'm not 100% sure, but I think the internal implementation of a Dictionary is a Hash-table, which means key's are converted to hashes to perform quick look ups.
Have a read here if you want to know more about hashtables
http://en.wikipedia.org/wiki/Hash_table
I have a the following dictionary:
IDictionary<int, IList<MyClass>> myDictionary
and I am wanting to get all the values in the dictionary as an IList....
Just to add a bit of a background as to how I've gotten into this situation....
I have a method that gets me a list of MyClass. I then have another method that converts that list into a dictionary where they key is the id for MyClass. Later on...and without access to that original list...I'm needing to obtain the original ungrouped list of MyClass.
When I pass myDictionary.Values.ToList() to a method that takes an IList I get a compile error that says that it can't convert from
System.Collections.Generic.List<System.Collections.Generic.IList<MyClass>>
to:
System.Collections.Generic.IList<MyClass>
Now, I can understand that its gone and added each of the groups of IList to the new list as separate elements of the list....but in this instance its not really what I'm after. I just want a list of all the values in the entire dictionary.
How then can I get what I'm after without looping through each of the key values in the dictionary and creating the list I want?
Noticed a lot of answer were quite old.
This will also work:
using System.Linq;
dict.Values.ToList();
Because of how a dictionary (or hash table) is maintained this is what you would do. Internally the implementation contains keys, buckets (for collision handling) and values. You might be able to retrieve the internal value list but you're better of with something like this:
IDictionary<int, IList<MyClass>> dict;
var flattenList = dict.SelectMany( x => x.Value );
It should do the trick ;) SelectMany flattens the result which means that every list gets concatenated into one long sequence (IEnumerable`1).
A variation on John's suggestion:
var flattenedValues = dict.Values.SelectMany(x => x);
If you need them in a list, you can of course call ToList:
var flattenedList = dict.Values.SelectMany(x => x).ToList();
dictionary.values.toList();
if You want to get Sum just do
myDictionary.values.sum();
Values gets a ICollection containing the values of your dictionary. As implied by the definition of your dictionary, it can be defined as a ICollection<IList<MyClass>> collection. So if you really want a IList<IList<MyClass>>, use spacedog's solution.
If what you really want is a flat `IList', then there is no other solution than looping through each value :
IList<MyClass> l=new List<MyClass>();
foreach (IList<MyClass> v in myDictionary.Values)
l.AddRange(v);
Note that this is so grossly inefficient that you should think again about using a dictionary for what you are trying to achieve.