I'm working on an approach to have a collection that efficiently can search based on more than one property. The sample code of the approach:
class SampleCollection
{
Dictionary<Sample, Sample> _dictItems;
public SampleCollection()
{
_dictItems = new Dictionary<Sample, Sample>(new SampleEqualityComparer());
}
public Sample FindById(int id)
{
return _dictItems[new Sample(id, string.Empty)];
}
public Sample FindByName(string name)
{
return _dictItems[new Sample(-1, name)];
}
}
class Sample
{
public Sample(int id, string name)
{
Id = id;
Name = name;
}
public int Id { get; set; }
public string Name { get; set; }
public string ALotOfOtherProperties { get; set; }
}
class SampleEqualityComparer : IEqualityComparer<Sample>
{
public bool Equals(Sample x, Sample y)
{
if (x.Id >= 0 && y.Id >= 0)
{
return x.Id == y.Id;
}
return x.Name.Equals(y.Name, StringComparison.CurrentCultureIgnoreCase);
}
public int GetHashCode(Sample obj)
{
//try with only name now
return obj.Name.GetHashCode();
//return 0;
}
}
This approach works perfectly fine as long as the Name property is not modified. Understandably, the Hash value no longer matches the original item in the Dictionary when the Name is modified.
Is it possible to force the Dictionary to recalculate the hash of its keys or any other workaround if it is not possible directly.?
It is really a performance hit when using a custom class as a key. The handling can take a 10 times longer.
I suggest that you have a dictionary for name and one for id.
I recommend that you set your Name and Id setter to private like:public string Name { get; private set; }
class SampleCollection
{
public SampleCollection()
{
NameLookup = new Dictionary<string, List<Sample>>();
IdLookup = new Dictionary<int, Sample>();
}
private Dictionary<string, List<Sample>> NameLookup;
private Dictionary<int, Sample> IdLookup;
public void Add(Sample sample)
{
IdLookup.Add(sample.Id, Sample);
List<Sample> list;
if (!NameLookup.TryGetValue(sample.Name, out list))
NameLookup.Add(sample.Name, list = new List<Sample>());
list.Add(Sample);
}
public Sample FindById(int id)
{
Sample result;
IdLookup.TryGetValue(id, out result);
return result;
}
public IEnumerable<Sample> FindByName(string name)
{
List<Sample> list;
if (NameLookup.TryGetValue(name, out list))
foreach(var sample in list)
yield return sample;
}
}
Related
I have a class that I've created
public class DataRecord
{
public string PayerAccount { get; set; }
public string GlobalEntityType { get; set; }
public string GlobalEntityNumber { get; set; }
}
I am now trying to access this DataRecord in a different method through the use of a variable
public List<DataTest> CountAndFrequency(IEnumerable records, string ColumnName, int numResults)
{
foreach (DataRecord record in records)
{
record.ColumnName = record.ColumnName.ToUpper();
}
}
I am getting the error that DataRecord does not contain a definition for ColumnName, which of course makes sense. The question is, how do I combat this issue? I've been scouring the internet to no avail and would appreciate any help.
Thanks in advance!
You can use reflection for this. Try this
public static List<DataTest> CountAndFrequency(IEnumerable<DataRecord> records, string ColumnName, int numResults)
{
foreach (DataRecord record in records)
{
var prop = typeof(DataRecord).GetProperty(ColumnName);
var value = prop.GetValue(record).ToString().ToUpper();
prop.SetValue(record, value);
}
}
If you want to access data via a string name, you store the data in a Dictionary<string,string>.
public class DataRecord
{
private readonly Dictionary<string, string> data;
public DataRecord()
{
this.data = new Dictionary<string, string>();
}
// Access data with names
public string this[string columnName]
{
get{ return data[columnName]; }
set{ data[columnName] = value;}
}
// Fake properties
public string PayerAccount
{
get => data[nameof(PayerAccount)];
set => data[nameof(PayerAccount)] = value;
}
public string GlobalEntityType
{
get => data[nameof(GlobalEntityType)];
set => data[nameof(GlobalEntityType)] = value;
}
public string GlobalEntityNumber
{
get => data[nameof(GlobalEntityNumber)];
set => data[nameof(GlobalEntityNumber)] = value;
}
}
class Program
{
static void Main(string[] args)
{
var record = new DataRecord
{
PayerAccount = "10024",
GlobalEntityType = "QXT",
GlobalEntityNumber = "509382"
};
var number = record["GlobalEntityNumber"];
// 509382
}
}
So that's my function:
public bool CheckUniqueName<T>(string newName, List<T> list)
{
for (int i = 0; i < list.Count(); i++)
{
if (list[i].name == newName)
{
return false;
}
}
return true;
}
I have this List of Planets: private List<Planet> planetsList = new List<Planet>();
BUT: I'm gonna use other Lists like public List<Colony> ColonyList = new List<Colony>(); That's why I need List<T>
And class Planet:
class Planet
{
...
public string name { get; }
...
}
And I try this: (some stuff) CheckUniqueName(name, planetsList) in other class
As I get it, List<T> doesn't know about the .name attribute.
I tried to create another List and do something like this:
public bool CheckUniqueName<T>(string newName, List<T> list)
{
if (list is List<Planet>)
{
var newList = planetsList;
}
for (int i = 0; i < list.Count(); i++)
{
if (list[i].name == newName)
{
return false;
}
}
return true;
}
It didn't work and same things with creating new List didn't work as well.
You can using generic constraints here:
public bool CheckUniqueName<T>(string newName, IEnumerable<T> items)
where T : INamed
=> !items.Any(i => (i.Name == newName));
public interface INamed
{
public Name { get; }
}
public class Planet : INamed
{
public Name { get; }
public Plant(string name)
{
Name = name;
}
}
public class Colony : INamed
{
public Name { get; }
public Colony(string name)
{
Name = name;
}
}
Another way to do this is to pass a delegate which knows how to fetch the name property off any type you pass in:
public bool CheckUniqueName<T>(IEnumerable<T> items, string newName, Func<T, string> nameSelector)
{
foreach (var item in items)
{
string name = nameSelector(item);
if (name == newName)
{
return false;
}
}
return true;
}
Call it like this:
CheckUniqueName(planetsList, "name", planet => planet.name);
Then your name property doesn't have to be called name -- it can be called whatever you want.
I wrote a long version of the CheckUniqueName method for clarity, but you could shorten it using linq:
public bool CheckUniqueName<T>(IEnumerable<T> items, string newName, Func<T, string> nameSelector)
{
return !items.Any(item => newName == nameSelector(item));
}
However once you go this far, you might as well discard the CheckUniqueName method entirely, and instead just write:
!plantsList.Any(x => x.name == "name");
This question already has answers here:
Getting hash of a list of strings regardless of order
(5 answers)
Closed 8 years ago.
Let's say I have a class
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
}
and I have a collection class that is simply a strongly typed List
public class MyClassList : List<MyClass>
{
public MyClassList(IEnumerable<MyClass> enumerable) : base (enumerable) {}
}
I want MyClassList to be able to generate a unique hash-code for MyClassList based on the contents. The hash-code of MyClass should be based on both properties. The hash-code of MyClassList should be the same even if the order of the objects is different.
To handle the ordering issue I was thinking I could order the list before generating the hash-code, but I'm not sure how to generate the hash-code of the list.
For optimal performance I would try to avoid iterating the whole collection every time GetHashCode is called. The purpose of GetHashCode is to improve performance to a point better than evaluating every element. So I might try maintaining the hash code when elements in the list are changed like this.
class Program
{
static void Main(string[] args)
{
MyClassList l = new MyClassList() { new MyClass() {Type="Bob", Id=1}, new MyClass() {Type="Jones", Id=2}};
MyClassList l2 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }, new MyClass() { Type = "Bob", Id = 1 } };
MyClassList l3 = new MyClassList() { new MyClass() { Type = "Jones", Id = 2 }};
Console.WriteLine("{0} {1} {2}", l.GetHashCode(), l2.GetHashCode(), l3.GetHashCode());
l3.Add(new MyClass() { Type = "Bob", Id = 1 });
Console.WriteLine("{0}", l3.GetHashCode());
}
}
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
public override int GetHashCode()
{
return (Type.GetHashCode() % 0x8000) | (int)((uint)Id.GetHashCode() & 0xFFFF0000);
}
}
public class MyClassList : IList<MyClass>
{
List<MyClass> internalList;
int hashCode = 0;
public MyClassList()
{
internalList = new List<MyClass>();
}
private void IncludeInHash(MyClass item)
{
hashCode ^= item.GetHashCode();
}
private void ExcludeFromHash(MyClass item)
{
IncludeInHash(item);
}
public override int GetHashCode()
{
return hashCode;
}
public int IndexOf(MyClass item)
{
return internalList.IndexOf(item);
}
public void Insert(int index, MyClass item)
{
internalList.Insert(index, item);
// Make sure Insert is successful (doesn't throw an exception) before affecting the hash
IncludeInHash(item);
}
public void RemoveAt(int index)
{
MyClass reduce = internalList[index];
internalList.RemoveAt(index);
// Make sure RemoveAt is successful before affecting the hash
ExcludeFromHash(reduce);
}
public MyClass this[int index]
{
get
{
return internalList[index];
}
set
{
MyClass reduce = internalList[index];
internalList[index] = value;
// Make sure these happen atomically; don't allow exceptions to prevent these from being accurate.
ExcludeFromHash(reduce);
IncludeInHash(value);
}
}
public void Add(MyClass item)
{
internalList.Add(item);
IncludeInHash(item);
}
public void Clear()
{
internalList.Clear();
hashCode = 0;
}
public bool Contains(MyClass item)
{
return internalList.Contains(item);
}
public void CopyTo(MyClass[] array, int arrayIndex)
{
internalList.CopyTo(array, arrayIndex);
}
public int Count
{
get { return internalList.Count; }
}
public bool IsReadOnly
{
get { return false; }
}
public bool Remove(MyClass item)
{
if (internalList.Remove(item))
{
ExcludeFromHash(item);
return true;
}
else
return false;
}
public IEnumerator<MyClass> GetEnumerator()
{
return internalList.AsReadOnly().GetEnumerator();
}
System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
The solution given by clto works. Here is an alternative: sort the list by some total ordering (any ordering will do, as long as it is unambiguous). Then you can calculate the hash code using any normal means. You don't need order-independence. You could even use a cryptographic hash function.
I propose this solution (I didn't implement the Equals method) :
public class MyClass
{
public string Type { get; set; }
public int Id { get; set; }
public override int GetHashCode()
{
int hash = 17;
hash = hash + 23 * this.Type.GetHashCode();
hash = hash + 23 * this.Id.GetHashCode();
return hash;
}
}
public class MyClassList : List<MyClass>
{
public MyClassList(IEnumerable<MyClass> enumerable) : base(enumerable) { }
public override int GetHashCode()
{
return this.Aggregate(17, (state, current) => state * 23 + current.GetHashCode());
}
}
The way to generate the hashcode is inspired from Microsoft method to compute the hash value for anonymous objects.
If the order isn't important then you should use a collection that inherently is a set, rather than a list.
Also, it's generally best to not inherit from collections; use composition instead.
So for a collection you can use a HashSet, as it will have set semantics.
To have MyClass use both properties as it's identity just override it's equals and get hash code implementations, or create an IComparer<MyClass> if you can't or don't want to do that.
public class MyClass:IEquatable<MyClass>
{
public string Type { get; set; }
public int Id { get; set; }
public override bool Equals(object obj)
{
return Equals(obj as MyClass);
}
public bool Equals(MyClass other)
{
if (other == null)
return false;
return Type == other.Type &&
Id == other.Id;
}
public override int GetHashCode()
{
return Type.GetHashCode() * 79 + Id;
}
}
Then your collection is as simple as:
HashSet<MyClass> set = new HashSet<MyClass>();
And if you want to compare various sets just use:
HashSet<MyClass>.CreateSetComparer();
Here is a Basic Class with TheProperty in question:
class BasicClass {
public BasicClass() {
TheProperty = new Object();
Stamped = DateTime.Now;
}
public object TheProperty { get; set; }
public DateTime Stamped { get; private set; }
}
Here is the Basic List:
class BasicList {
private List<BasicClass> list;
public BasicList() {
list = new List<BasicClass>();
}
public BasicClass this[object obj] {
get { return list.SingleOrDefault(o => o.TheProperty == obj); }
}
public void Add(BasicClass item) {
if (!Contains(item.TheProperty)) {
list.Add(item);
}
}
public bool Contains(object obj) {
return list.Any(o => o.TheProperty == obj); // Picked this little gem up yesterday!
}
public int Count { get { return list.Count; } }
}
I'd like to add a class to BasicList that will return an array of items.
I could write it like this, using traditional C#:
public object[] Properties() {
var props = new List<Object>(list.Count);
foreach (var item in list) {
props.Add(item.TheProperty);
}
return props.ToArray();
}
...but how would I write that using a LINQ or Lambda query?
return list.Select(p=>p.TheProperty).ToArray()
This is a entity and i want to list all the children node for a given node in a generic function
public static List<T> BuildTree<T>(List<T> list, T selectNode string keyPropName, string parentPropName, string levelPropName, int level = 0)
{
List<T> entity = new List<T>();
foreach (T item in list)
{
}
return entity;
}
example of the entity structure
protected long _coakey;
protected long _parentkey;
protected string _coacode;
protected string _coacodeclient;
protected string _coaname;
protected int _coalevel;
[DataMember]
public long coakey
{
get { return _coakey; }
set { _coakey = value; this.OnChnaged(); }
}
[DataMember]
public long parentkey
{
get { return _parentkey; }
set { _parentkey = value; this.OnChnaged(); }
}
[DataMember]
public string coacode
{
get { return _coacode; }
set { _coacode = value; this.OnChnaged(); }
}
[DataMember]
public string coacodeclient
{
get { return _coacodeclient; }
set { _coacodeclient = value; this.OnChnaged(); }
}
[DataMember]
public string coaname
{
get { return _coaname; }
set { _coaname = value; this.OnChnaged(); }
}
[DataMember]
public int coalevel
{
get { return _coalevel; }
set { _coalevel = value; this.OnChnaged(); }
}
Your BuildTree<T> method cannot determine the structure of the tree unless it knows something about its structure. At a very minimum, I would suggest making a base class or interface that defines a tree node, and then change the BuildTree method to work specifically with those types of objects. Then, it will be able to figure out the tree structure. Each of you entity classes would have to implement that tree node interface or inherit from the tree node base class. For instance:
public abstract class TreeNodeBase
{
public long parentkey
{
get { return _parentkey; }
set { _parentkey = value; this.OnChanged(); }
}
protected long _parentkey;
}
public class MyEntityTreeNode : TreeNodeBase
{
public long coakey
{
get { return _coakey; }
set { _coakey = value; this.OnChanged(); }
}
protected long _coakey;
// etc...
}
// Note the generic type constraint at the end of the next line
public static List<T> BuildTree<T>(List<T> list, T selectNode, string keyPropName, string parentPropName, string levelPropName, int level) where T : TreeNodeBase
{
List<T> entity = new List<T>();
foreach (TreeNodeBase node in list)
{
long parentKey = node.parentkey;
// etc...
}
return entity;
}
Node class:
public class Node<TKey, TValue> where TKey : IEquatable<TKey>
{
public TKey Key { get; set; }
public TKey ParentKey { get; set; }
public TValue Data { get; set; }
public readonly List<Node<TKey, TValue>> Children = new List<Node<TKey, TValue>>();
}
TreeBuilder:
public static Node<TKey, TValue> BuildTree<TKey, TValue>(IEnumerable<Node<TKey, TValue>> list,
Node<TKey, TValue> selectNode)
where TKey : IEquatable<TKey>
{
if (ReferenceEquals(selectNode, null))
{
return null;
}
var selectNodeKey = selectNode.Key;
foreach (var childNode in list.Where(x => x.ParentKey.Equals(selectNodeKey)))
{
selectNode.Children.Add(BuildTree(list, childNode));
}
return selectNode;
}
Usage:
List<MyClass> list = ...
var nodes = list.Select(x => new Node<long, MyClass>
{
Key = x.MyKey,
ParentKey = x.MyParentKey,
Data = x
}).ToList();
var startNode = nodes.FirstOrDefault(x => x.Data.Stuff == "Pick me!");
var tree = BuildTree(nodes, startNode);
MyClass example:
public class MyClass
{
public long MyKey;
public long MyParentKey;
public string Name;
public string Text;
public string Stuff;
}
I have solved it my self hope it help you
public static List<T> BuildTree<T>(List<T> list, T selectedNode, string keyPropName, string parentPropName, int endLevel = 0, int level = 0)
{
List<T> entity = new List<T>();
Type type = typeof(T);
PropertyInfo keyProp = type.GetProperty(keyPropName);
string _selectedNodekey = keyProp.GetValue(selectedNode, null).ToString();
PropertyInfo parentProp = type.GetProperty(parentPropName);
foreach (T item in list)
{
string _key = keyProp.GetValue(item, null).ToString();
string _parent = parentProp.GetValue(item, null).ToString();
if (_selectedNodekey == _parent)
{
T obj = (T)Activator.CreateInstance(typeof(T));
obj = item;
entity.Add(obj);
if (level == endLevel && level!=0) break;
entity.AddRange(BuildTree<T>(list, obj, keyPropName, parentPropName, level + 1));
}
}
return entity;
}