After click over row in DataGridView I take value of two cells in this row:
string id = Convert.ToString(dataGridView1.Rows[e.RowIndex].Cells["Number"].Value);
string type = Convert.ToString(dataGridView1.Rows[e.RowIndex].Cells["dataGridViewTextBoxColumn46"].Value);
So, in which structure to store these values, that to take off them further?
In result I need to compare if id, type are exist in structure.
I tried Dictionary<int, int>. But it is hard to check if there values are in Dictionary like this: Dictionary<'id', 'type'>
A simple HashSet<Tuple<string, string>> would probably do:
HashSet<T> is a set of values which provides O(1) average lookup time for "contains" queries.
Tuple<T1, T2> is a class representing a pair of values, which uses value-type equality semantics, i.e. implements Equals and GetHashCode using the values stored inside the class, meaning that two different instances with same members will be considered equal (and this is important if you want to use them as HashSet<T> keys.
So, you would simply do something like:
// somewhere in your method or class
HashSet<Tuple<string, string>> hashset = new HashSet<Tuple<string, string>>();
// once you get the (id, type) pair:
hashset.Add(Tuple.Create(id, key));
// to check if the items are in the hashset:
if (hashset.Contains(Tuple.Create("a", "b"))
{
// do stuff
}
// to remove the item from the hashset
hashset.Remove(Tuple.Create("a", "b"));
I am having trouble trying to iterate over a dictionary passed to a function as a generic. For example, I have a function that loads data from a DB.
public T Load<T>(...)
This function can be called like so, with which I have no problems;
someclasstype data = Load<someclasstype>(...);
List<someclasstype> data = Load<List<someclasstype>>(...);
I've recently tried to extend this to be able to deal with dictionaries as well, and calling it like so:
Dictionary<long, someclasstype> data = Load<Dictionary<long, someclasstype>>(...)
I can load the data without a problem and store it in the dictionary no problem.
At this stage, the dictionary, with all its keyvaluepairs is stored in a variable called result, and I'm creating an IEnumerable with
IEnumerator resultIdx = ((IEnumerable)result).GetEnumerator();
if (!resultIdx.MoveNext())
return (T)result;
object kvp = resultIdx.Current;
So far so good. I can see the value of the key and the value of the value in a watch, or by mouseover on the kvp variable.
But I cannot figure out how to get the value part of the keyvaluepair from kvp.
// None of these work - I get compile time errors, unboxing errors, or invalid cast errors.
object item = ((KeyValuePair<TKey, TValue>)kvp).Value;
object item = ((KeyValuePair<long, object>)kvp).Value;
object item = ((T)kvp).Value // Never had a hope for this, but desperation...
Does anyone have any idea how I can do this?
try adding dynamic kvp = resultIdx.Current; . Then you can use kvp.Value
You can rewrite the function into two functions like.
public T Load<T>(...)
//Or maybe public List<T> Load<T>(...)
and
public Dictionary<long, T> LoadD<T>(...)
Then you can cast result to KeyValuePair<long, T> in LoadD. You can call Load from LoadD to minimize code rewriting.
Answer provided by Dede in comments:
"Use Reflection ?
object key kvp.GetType().GetProperty("Key").GetValue(kvp);
object value kvp.GetType().GetProperty("Value").GetValue(kvp);
Not very optimized, but can work... – Dede 24"
I know I can use a foreach loop as follows:
List<int> handles = GetHandles();
foreach (int handle in handles)
{
// do stuff
}
Can I do the same for a SortedList as follows?
SortedList<string, int> namesAndHandles;
EDIT: Sorry, made a typo. It should be a SortedList. Essentially I want to convert this to an IDictionary and access the handles based off a name
There's no such thing as List<string, int> - there's no List<,> type with two type parameters. If you've got a collection of name/handle pairs, you should either use List<Tuple<string, int>> or create your own NameAndHandle class. Either will work fine with foreach.
(You could create your own List<TFirst, TSecond> class if you really wanted, but I'd really advise against it.)
I bet List<KeyValuePair<string,int>> would do what you are looking for. You could iterate the collection and the .Key property holds the string and .Value holds the int
The whole story; I have some KeyValuePairs that I need to store in a session and my primary goal is to keep it small. Therefore I don't have the option of using many different collection. While the key is a different enum value of of a different enum type the value is always just a enum value of the same enum type. I have chosen a HashTable for this approach which content look like this (just many more):
// The Key-Value-Pairs
{ EnumTypA.ValueA1, MyEnum.ValueA },
{ EnumTypB.ValueB1, MyEnum.ValueB },
{ EnumTypC.ValueC1, MyEnum.ValueA },
{ EnumTypA.ValueA2, MyEnum.ValueC },
{ EnumTypB.ValueB1, MyEnum.ValueC }
At most I am running contains on that HashTable but for sure I also need to fetch the value at some point and I need to loop through all elements. That all works fine but now I have a new requirement to keep the order I have added them to the HashTable -> BANG
A HashTable is a map and that is not possible!
Now I thought about using a SortedList<object, MyEnum> or to go with more Data but slightly faster lookups and use a SortedSet<object> in addition to the HashTable.
Content below has been edited
The SortedList is implemented as
SortedList<Enum, MyEnum> mySortedList = new SortedList<Enum, MyEnum>();
the SortedSet is implemented as
SortedSet<Enum> mySortedSet = new SortedSet<Enum>();
The described Key - Value - Pairs are added to the sorted list with
void AddPair(Enum key, MyEnum value)
{
mySortedList.Add(key, value);
}
And for the SortedSett like this
void AddPair(Enum key)
{
mySortedSet.Add(key);
}
Both are failing with the exception:
Object must be the same type as the
enum
My question is: What goes wrong and how can I archive my goal?
Used Solution
I've decided to life with the downside
of redundant data against slower
lookups and decided to implement a
List<Enum> which will retain the
insert order parallel to my already
existing HashTable.
In my case I just have about 50-150
Elements so I decided to benchmark the
Hashtable against the
List<KeyValuePair<object,object>>
Therefore I have create me the
following helper to implement
ContainsKey() to the
List<KeyValuePair<object,object>>
static bool ContainsKey(this List<KeyValuePair<object, object>> list, object key)
{
foreach (KeyValuePair<object, object> p in list)
{
if (p.Key.Equals(key))
return true;
}
return false;
}
I inserted the same 100 Entries and
checked randomly for one of ten
different entries in a 300000 loop.
And... the difference was tiny so I
decided to go with the
List<KeyValuePair<object,object>>
I think you should store your data in an instance of List<KeyValuePair<Enum, MyEnum>> or Dictionary<Enum, MyEnum>.
SortedSet and SortedList are generic, but your keys are EnumTypeA/EnumTypeB, you need to specify the generic T with their base class(System.Enum) like:
SortedList<Enum, MyEnum> sorted = new SortedList<Enum, MyEnum>();
EDIT
Why you got this exception
SortedList and SortedSet use a comparer inside to check if two keys are equal. Comparer<Enum>.Default will be used as the comparer if you didn't specify the comparer in the constructor. Unfortunately Comparer<Enum>.Default isn't implemented as you expected. It throws the exception if the two enums are not the same type.
How to resolve the problem
If you don't want to use a List<KeyValuePair<Enum, MyEnum>> and insist using SortedLIst, you need to specify a comparer to the constructor like this:
class EnumComparer : IComparer<Enum>
{
public int Compare(Enum x, Enum y)
{
return x.GetHashCode() - y.GetHashCode();
}
}
var sorted = new SortedList<Enum, MyEnum>(new EnumComparer());
Btw, I think you need to obtain the "inserting order"? If so, List<KeyValuePair<K,V>> is a better choice, because SortedSet will prevent duplicated items.
I'm using a Dictionary<string, int> where the int is a count of the key.
Now, I need to access the last-inserted Key inside the Dictionary, but I do not know the name of it. The obvious attempt:
int LastCount = mydict[mydict.keys[mydict.keys.Count]];
does not work, because Dictionary.Keys does not implement a []-indexer.
I just wonder if there is any similar class? I thought about using a Stack, but that only stores a string. I could now create my own struct and then use a Stack<MyStruct>, but I wonder if there is another alternative, essentially a Dictionary that implements an []-indexer on the Keys?
As #Falanwe points out in a comment, doing something like this is incorrect:
int LastCount = mydict.Keys.ElementAt(mydict.Count -1);
You should not depend on the order of keys in a Dictionary. If you need ordering, you should use an OrderedDictionary, as suggested in this answer. The other answers on this page are interesting as well.
You can use an OrderedDictionary.
Represents a collection of key/value
pairs that are accessible by the key
or index.
A Dictionary is a Hash Table, so you have no idea the order of insertion!
If you want to know the last inserted key I would suggest extending the Dictionary to include a LastKeyInserted value.
E.g.:
public MyDictionary<K, T> : IDictionary<K, T>
{
private IDictionary<K, T> _InnerDictionary;
public K LastInsertedKey { get; set; }
public MyDictionary()
{
_InnerDictionary = new Dictionary<K, T>();
}
#region Implementation of IDictionary
public void Add(KeyValuePair<K, T> item)
{
_InnerDictionary.Add(item);
LastInsertedKey = item.Key;
}
public void Add(K key, T value)
{
_InnerDictionary.Add(key, value);
LastInsertedKey = key;
}
.... rest of IDictionary methods
#endregion
}
You will run into problems however when you use .Remove() so to overcome this you will have to keep an ordered list of the keys inserted.
Why don't you just extend the dictionary class to add in a last key inserted property. Something like the following maybe?
public class ExtendedDictionary : Dictionary<string, int>
{
private int lastKeyInserted = -1;
public int LastKeyInserted
{
get { return lastKeyInserted; }
set { lastKeyInserted = value; }
}
public void AddNew(string s, int i)
{
lastKeyInserted = i;
base.Add(s, i);
}
}
You could always do this:
string[] temp = new string[mydict.count];
mydict.Keys.CopyTo(temp, 0)
int LastCount = mydict[temp[mydict.count - 1]]
But I wouldn't recommend it. There's no guarantee that the last inserted key will be at the end of the array. The ordering for Keys on MSDN is unspecified, and subject to change. In my very brief test, it does seem to be in order of insertion, but you'd be better off building in proper bookkeeping like a stack--as you suggest (though I don't see the need of a struct based on your other statements)--or single variable cache if you just need to know the latest key.
I think you can do something like this, the syntax might be wrong, havent used C# in a while
To get the last item
Dictionary<string, int>.KeyCollection keys = mydict.keys;
string lastKey = keys.Last();
or use Max instead of Last to get the max value, I dont know which one fits your code better.
I agree with the second part of Patrick's answer. Even if in some tests it seems to keep insertion order, the documentation (and normal behavior for dictionaries and hashes) explicitly states the ordering is unspecified.
You're just asking for trouble depending on the ordering of the keys. Add your own bookkeeping (as Patrick said, just a single variable for the last added key) to be sure. Also, don't be tempted by all the methods such as Last and Max on the dictionary as those are probably in relation to the key comparator (I'm not sure about that).
In case you decide to use dangerous code that is subject to breakage, this extension function will fetch a key from a Dictionary<K,V> according to its internal indexing (which for Mono and .NET currently appears to be in the same order as you get by enumerating the Keys property).
It is much preferable to use Linq: dict.Keys.ElementAt(i), but that function will iterate O(N); the following is O(1) but with a reflection performance penalty.
using System;
using System.Collections.Generic;
using System.Reflection;
public static class Extensions
{
public static TKey KeyByIndex<TKey,TValue>(this Dictionary<TKey, TValue> dict, int idx)
{
Type type = typeof(Dictionary<TKey, TValue>);
FieldInfo info = type.GetField("entries", BindingFlags.NonPublic | BindingFlags.Instance);
if (info != null)
{
// .NET
Object element = ((Array)info.GetValue(dict)).GetValue(idx);
return (TKey)element.GetType().GetField("key", BindingFlags.Public | BindingFlags.Instance).GetValue(element);
}
// Mono:
info = type.GetField("keySlots", BindingFlags.NonPublic | BindingFlags.Instance);
return (TKey)((Array)info.GetValue(dict)).GetValue(idx);
}
};
One alternative would be a KeyedCollection if the key is embedded in the value.
Just create a basic implementation in a sealed class to use.
So to replace Dictionary<string, int> (which isn't a very good example as there isn't a clear key for a int).
private sealed class IntDictionary : KeyedCollection<string, int>
{
protected override string GetKeyForItem(int item)
{
// The example works better when the value contains the key. It falls down a bit for a dictionary of ints.
return item.ToString();
}
}
KeyedCollection<string, int> intCollection = new ClassThatContainsSealedImplementation.IntDictionary();
intCollection.Add(7);
int valueByIndex = intCollection[0];
The way you worded the question leads me to believe that the int in the Dictionary contains the item's "position" on the Dictionary. Judging from the assertion that the keys aren't stored in the order that they're added, if this is correct, that would mean that keys.Count (or .Count - 1, if you're using zero-based) should still always be the number of the last-entered key?
If that's correct, is there any reason you can't instead use Dictionary<int, string> so that you can use mydict[ mydict.Keys.Count ]?
I don't know if this would work because I'm pretty sure that the keys aren't stored in the order they are added, but you could cast the KeysCollection to a List and then get the last key in the list... but it would be worth having a look.
The only other thing I can think of is to store the keys in a lookup list and add the keys to the list before you add them to the dictionary... it's not pretty tho.
To expand on Daniels post and his comments regarding the key, since the key is embedded within the value anyway, you could resort to using a KeyValuePair<TKey, TValue> as the value. The main reasoning for this is that, in general, the Key isn't necessarily directly derivable from the value.
Then it'd look like this:
public sealed class CustomDictionary<TKey, TValue>
: KeyedCollection<TKey, KeyValuePair<TKey, TValue>>
{
protected override TKey GetKeyForItem(KeyValuePair<TKey, TValue> item)
{
return item.Key;
}
}
To use this as in the previous example, you'd do:
CustomDictionary<string, int> custDict = new CustomDictionary<string, int>();
custDict.Add(new KeyValuePair<string, int>("key", 7));
int valueByIndex = custDict[0].Value;
int valueByKey = custDict["key"].Value;
string keyByIndex = custDict[0].Key;
A dictionary may not be very intuitive for using index for reference but, you can have similar operations with an array of KeyValuePair:
ex.
KeyValuePair<string, string>[] filters;
You can also use SortedList and its Generic counterpart. These two classes and in Andrew Peters answer mentioned OrderedDictionary are dictionary classes in which items can be accessed by index (position) as well as by key. How to use these classes you can find: SortedList Class , SortedList Generic Class .
Visual Studio's UserVoice gives a link to generic OrderedDictionary implementation by dotmore.
But if you only need to get key/value pairs by index and don't need to get values by keys, you may use one simple trick. Declare some generic class (I called it ListArray) as follows:
class ListArray<T> : List<T[]> { }
You may also declare it with constructors:
class ListArray<T> : List<T[]>
{
public ListArray() : base() { }
public ListArray(int capacity) : base(capacity) { }
}
For example, you read some key/value pairs from a file and just want to store them in the order they were read so to get them later by index:
ListArray<string> settingsRead = new ListArray<string>();
using (var sr = new StreamReader(myFile))
{
string line;
while ((line = sr.ReadLine()) != null)
{
string[] keyValueStrings = line.Split(separator);
for (int i = 0; i < keyValueStrings.Length; i++)
keyValueStrings[i] = keyValueStrings[i].Trim();
settingsRead.Add(keyValueStrings);
}
}
// Later you get your key/value strings simply by index
string[] myKeyValueStrings = settingsRead[index];
As you may have noticed, you can have not necessarily just pairs of key/value in your ListArray. The item arrays may be of any length, like in jagged array.