I'm trying to get a reference on a sub array from a existing array.
I want to be able to update the original array when i'm doing a modification on the sub array.
Example :
byte[] array = {0 , 1, 2, 3, 4};
byte[] subarray = array.Skip(2).Take(3).ToArray();
subarray[0] = 8;
Console.WriteLine("array[2] = " + array[2]);
I want to see :
array[2] = 8
but instead, i get :
array[2] = 2
I read this solution but its not good enough because I dont want to give the option to modify array values that are not in the range, like this :
ArraySegment<byte> segment = new ArraySegment<byte>(array, 2, 3);
byte[] segmentByte = segment.ToArray();
I can modifiy all the original array through segmentByte. This is what i want to prevent.
You can write simple Array and ArraySegment<of T> wrapper that provides set of required operations only:
struct StrictRangeArraySegment<T>
{
ArraySegment<T> _segment;
public StrictRangeArraySegment(T[] array)
: this(array, 0, array.Length)
{
}
public StrictRangeArraySegment(T[] array, int offset, int count)
: this(new ArraySegment<T>(array, offset, count))
{
}
public StrictRangeArraySegment(ArraySegment<T> segment)
{
_segment = segment;
}
public int Count
{
get
{
return _segment.Count;
}
}
public T this[int index]
{
get
{
if (index < 0 || index >= _segment.Count)
throw new ArgumentOutOfRangeException(nameof(index));
return _segment.Array[_segment.Offset + index];
}
set
{
if (index < 0 || index >= _segment.Count)
throw new ArgumentOutOfRangeException(nameof(index));
_segment.Array[_segment.Offset + index] = value;
}
}
}
For reference see ArraySegment<Of T> source code.
If you take a closer look at ToList method, you will see that it completely generate a new list which is not referred to the old one at all. So what you change only reflect to subarray only.
The only solution is to use that ArraySegment that you don't want to.
public List<TResult> ToList()
{
var list = new List<TResult>();
foreach (TSource item in _source)
{
list.Add(_selector(item));
}
return list;
}
One option is creating a type to box your integers as a property of an object. Then updating the property will have the desired result:
public class Box<T>
{
public T Value {get;set;}
public Box<T>(T item) {Value = item;}
}
Box<byte>[] array = {new Box<byte>(0), new Box<byte>(1), new Box<byte>(2), new Box<byte>(3), new Box<byte>(4)};
Box<byte>[] subarray = array.Skip(2).Take(3).ToArray();
subarray[0].Value = 8;
Console.WriteLine("array[2] = " + array[2].Value);
//you'll see "8" instead of "2" now
You might also want to look at Span<T>. It's not fully released yet, but it might make it possible to accomplish your goal here.
I have to store two types of information in any data structure for what I came up with the scrap solution of 2D array in C#. I have to store as:
number of cluster in int data type
cluster membership count in int data type
If I use a 2D array as:
Int32[,] _clusterMembership = new Int32[10, 10];
But the issue here is:
I don't know what total number of cluster will be?
I don't know what number of members each cluster will have?
So the question is:
How can I manage to store this information in C# ?
ADDENDUM
I have to use answer from this question here in this method as:
public static List<Cluster> DP_Cluster(List<string> _customer, double _alpha)
{
var _currentClusters = 0; // current number of clusters i.e. "k"
var _memberNumber = 0; // running member number i.e. "n"
//var _dic = new Dictionary<int, List<string>>();
var _probOld = 0.0;
var _probNew = 0.0;
List<Cluster> myClusters = new List<Cluster>();
Cluster cluster = new Cluster(_currentClusters += 1);
cluster.Members.Add(new ClusterMember { Name = _customer.ElementAt(_memberNumber) });
myClusters.Add(cluster);
//_dic.Add(_currentClusters, _customer.ElementAt(_memberNumber));
_currentClusters += 1;
for(int _i = 1; _i < _customer.Count - 1; _i++)
{
if( _i <= _currentClusters)
{
_probOld = myClusters[_i].Members.Count / ((_i+1) - 1 + _alpha);
}
else
{
_probNew = _alpha / ((_i+1) - 1 + _alpha);
}
if(_probNew > _probOld)
{
// Add _customer.ElementAt(_memberNumber+=1) to New Cluster
Cluster cluster = new Cluster( _currentClusters += 1 ); // Here is an error as we defining same name for another cluster
myClusters.Add(cluster);
}
else
{
// Add _customer.ElementAt(_memberNumber+=1) to Old Cluster
}
}
return myClusters;
}
How should I update my method to get desired results?
You should consider making two types, one for the clusters and one for the members:
Members
public class ClusterMember
{
public string Name {get;set;}
// more properties...
}
Clusters
public class Cluster
{
public int ID {get;}
public List<ClusterMember> Members {get;}
public Cluster(int id)
{
ID = id;
Members = new List<ClusterMember();
}
}
And then you can store your clusters in a list
List<Cluster> myClusters = new List<Cluster>();
Cluster cluster = new Cluster(1);
cluster.Members.Add(new ClusterMember { Name = "Member1" });
myClusters.Add(cluster);
UPDATE I assumed that you want to do more with your data than just store these two information and tried to provide a better object-oriented approach.
To get your counts:
int totalNumberOfClusters = myClusters.Count;
int numberOfMembersInOneCluster = cluster.Members.Count;
int totalNumberOfClusterMembers = myClusters.Sum(c => c.Members.Count);
And to output the number of members for each cluster:
foreach(Cluster c in myClusters)
Console.WriteLine($"Cluster {c.ID} has {c.Members.Count} members.");
As is already mentioned. You can simply use a list. The bottom code example shows how to create the list type you need and how you add and access values in that list.
using System.IO;
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
//Creating a list of lists that contains integers
List<List<int>> clusters = new List<List<int>>();
//each list in the above list consists of a list of integers. So we need to add list of integers to that list
List<int> row = new List<int>();
//now we add integers to the list
row.Add(1); row.Add(2); row.Add(3); row.Add(4);
//Now we add the list of integers to the list of lists of integers
clusters.Add(row);
foreach(List<int> rows in clusters)
{
foreach(int num in rows)
{
System.Console.WriteLine(num);
}
}
Console.WriteLine("number of rows: {0}", clusters.Count);
Console.WriteLine("number of elements in the first row: {0}", clusters[0].Count);
}
}
You could consider using a list of lists;
List<List<int>> clusters;
See this answer on another question for more info and also how to make it into a more generic class: https://stackoverflow.com/a/1596563/6065552
You can store your data in a list which has keyvaluepair items.
Or use Dictionary
List<KeyValuePair<int, int>>()
Dictionary<int,int>();
so you can add new keyvaluepair for each cluster.
static void Main(string[] args)
{
var clusterMembership = new Dictionary<int, int>();
//Add cluster 123 and assign a member count of 4
clusterMembership.Add(123, 4);
//Change member count for cluster 123 to 5
clusterMembership[123] = 5;
//Remove cluster 123
clusterMembership.Remove(123);
//Get the number of clusters in the dictionary
var count = clusterMembership.Count;
//Iterate through the dictionary
foreach(var clusterKey in clusterMembership.Keys)
{
var memberCount = clusterMembership[clusterKey];
}
}
I need to get an object and check if it already exists.
In case it does, I want to add a number, or increase the number in its name.
For example if I have the object "a" and it exists, I need to add a 1 so it's called a1.
In case a1 exists, a2, etc.
How could I perform this?
My code:
if (e.TreeNode.Tag is Variant)
{
if (variantExists(e.TreeNode.Text))
{
Random r = new Random();
int randomNumber = r.Next(0, 99);
e.TreeNode.Text = e.TreeNode.Text + randomNumber;
//e.TreeNode.Remove();
return;
}
}
Can you change the TreeNode class? I would add properties for Label (Name without Index) and Index and make the Name property read only, i.e
class TreeNode
{
public int Index {get;set;}
public string Label {get;set;}
public string Name
{
get { return Index == 0 ? Label : Label + Index; }
}
}
In your code you just need to set the Index property to the value you need and dont worry about the whole string parsing stuff
string name = "SomeName";
string tempName = name;
int n = 0;
while (DoesNameExist(tempName))
{
n++;
tempName = name + n;
}
name = tempName;
This gets ineffecient for large numbers of the same object, but that shouldn't happen right?
The problem with doing it the other way around, and stripping off trailing numbers to find the "original" name is that the original name may genuinely have numbers on it.
Eg. You say you add:
SomeName
SomeName99
SomeName
SomeName99
The above code will give you
SomeName
SomeName1
SomeName99
SomeName991
Something along the lines of this could work:
var existingItems = new HashSet<string>();
var items = new List<string>{"a", "b", "a"};
foreach (var item in items)
{
var tempItem = item;
var i = 1;
while (!existingItems.Add(tempItem))
tempItem = tempItem + i++;
}
Anyone have a quick method for de-duplicating a generic List in C#?
If you're using .Net 3+, you can use Linq.
List<T> withDupes = LoadSomeData();
List<T> noDupes = withDupes.Distinct().ToList();
Perhaps you should consider using a HashSet.
From the MSDN link:
using System;
using System.Collections.Generic;
class Program
{
static void Main()
{
HashSet<int> evenNumbers = new HashSet<int>();
HashSet<int> oddNumbers = new HashSet<int>();
for (int i = 0; i < 5; i++)
{
// Populate numbers with just even numbers.
evenNumbers.Add(i * 2);
// Populate oddNumbers with just odd numbers.
oddNumbers.Add((i * 2) + 1);
}
Console.Write("evenNumbers contains {0} elements: ", evenNumbers.Count);
DisplaySet(evenNumbers);
Console.Write("oddNumbers contains {0} elements: ", oddNumbers.Count);
DisplaySet(oddNumbers);
// Create a new HashSet populated with even numbers.
HashSet<int> numbers = new HashSet<int>(evenNumbers);
Console.WriteLine("numbers UnionWith oddNumbers...");
numbers.UnionWith(oddNumbers);
Console.Write("numbers contains {0} elements: ", numbers.Count);
DisplaySet(numbers);
}
private static void DisplaySet(HashSet<int> set)
{
Console.Write("{");
foreach (int i in set)
{
Console.Write(" {0}", i);
}
Console.WriteLine(" }");
}
}
/* This example produces output similar to the following:
* evenNumbers contains 5 elements: { 0 2 4 6 8 }
* oddNumbers contains 5 elements: { 1 3 5 7 9 }
* numbers UnionWith oddNumbers...
* numbers contains 10 elements: { 0 2 4 6 8 1 3 5 7 9 }
*/
How about:
var noDupes = list.Distinct().ToList();
In .net 3.5?
Simply initialize a HashSet with a List of the same type:
var noDupes = new HashSet<T>(withDupes);
Or, if you want a List returned:
var noDupsList = new HashSet<T>(withDupes).ToList();
Sort it, then check two and two next to each others, as the duplicates will clump together.
Something like this:
list.Sort();
Int32 index = list.Count - 1;
while (index > 0)
{
if (list[index] == list[index - 1])
{
if (index < list.Count - 1)
(list[index], list[list.Count - 1]) = (list[list.Count - 1], list[index]);
list.RemoveAt(list.Count - 1);
index--;
}
else
index--;
}
Notes:
Comparison is done from back to front, to avoid having to resort list after each removal
This example now uses C# Value Tuples to do the swapping, substitute with appropriate code if you can't use that
The end-result is no longer sorted
I like to use this command:
List<Store> myStoreList = Service.GetStoreListbyProvince(provinceId)
.GroupBy(s => s.City)
.Select(grp => grp.FirstOrDefault())
.OrderBy(s => s.City)
.ToList();
I have these fields in my list: Id, StoreName, City, PostalCode
I wanted to show list of cities in a dropdown which has duplicate values.
solution: Group by city then pick the first one for the list.
It worked for me. simply use
List<Type> liIDs = liIDs.Distinct().ToList<Type>();
Replace "Type" with your desired type e.g. int.
As kronoz said in .Net 3.5 you can use Distinct().
In .Net 2 you could mimic it:
public IEnumerable<T> DedupCollection<T> (IEnumerable<T> input)
{
var passedValues = new HashSet<T>();
// Relatively simple dupe check alg used as example
foreach(T item in input)
if(passedValues.Add(item)) // True if item is new
yield return item;
}
This could be used to dedupe any collection and will return the values in the original order.
It's normally much quicker to filter a collection (as both Distinct() and this sample does) than it would be to remove items from it.
An extension method might be a decent way to go... something like this:
public static List<T> Deduplicate<T>(this List<T> listToDeduplicate)
{
return listToDeduplicate.Distinct().ToList();
}
And then call like this, for example:
List<int> myFilteredList = unfilteredList.Deduplicate();
In Java (I assume C# is more or less identical):
list = new ArrayList<T>(new HashSet<T>(list))
If you really wanted to mutate the original list:
List<T> noDupes = new ArrayList<T>(new HashSet<T>(list));
list.clear();
list.addAll(noDupes);
To preserve order, simply replace HashSet with LinkedHashSet.
This takes distinct (the elements without duplicating elements) and convert it into a list again:
List<type> myNoneDuplicateValue = listValueWithDuplicate.Distinct().ToList();
Use Linq's Union method.
Note: This solution requires no knowledge of Linq, aside from that it exists.
Code
Begin by adding the following to the top of your class file:
using System.Linq;
Now, you can use the following to remove duplicates from an object called, obj1:
obj1 = obj1.Union(obj1).ToList();
Note: Rename obj1 to the name of your object.
How it works
The Union command lists one of each entry of two source objects. Since obj1 is both source objects, this reduces obj1 to one of each entry.
The ToList() returns a new List. This is necessary, because Linq commands like Union returns the result as an IEnumerable result instead of modifying the original List or returning a new List.
As a helper method (without Linq):
public static List<T> Distinct<T>(this List<T> list)
{
return (new HashSet<T>(list)).ToList();
}
Here's an extension method for removing adjacent duplicates in-situ. Call Sort() first and pass in the same IComparer. This should be more efficient than Lasse V. Karlsen's version which calls RemoveAt repeatedly (resulting in multiple block memory moves).
public static void RemoveAdjacentDuplicates<T>(this List<T> List, IComparer<T> Comparer)
{
int NumUnique = 0;
for (int i = 0; i < List.Count; i++)
if ((i == 0) || (Comparer.Compare(List[NumUnique - 1], List[i]) != 0))
List[NumUnique++] = List[i];
List.RemoveRange(NumUnique, List.Count - NumUnique);
}
Installing the MoreLINQ package via Nuget, you can easily distinct object list by a property
IEnumerable<Catalogue> distinctCatalogues = catalogues.DistinctBy(c => c.CatalogueCode);
If you have tow classes Product and Customer and we want to remove duplicate items from their list
public class Product
{
public int Id { get; set; }
public string ProductName { get; set; }
}
public class Customer
{
public int Id { get; set; }
public string CustomerName { get; set; }
}
You must define a generic class in the form below
public class ItemEqualityComparer<T> : IEqualityComparer<T> where T : class
{
private readonly PropertyInfo _propertyInfo;
public ItemEqualityComparer(string keyItem)
{
_propertyInfo = typeof(T).GetProperty(keyItem, BindingFlags.GetProperty | BindingFlags.Instance | BindingFlags.Public);
}
public bool Equals(T x, T y)
{
var xValue = _propertyInfo?.GetValue(x, null);
var yValue = _propertyInfo?.GetValue(y, null);
return xValue != null && yValue != null && xValue.Equals(yValue);
}
public int GetHashCode(T obj)
{
var propertyValue = _propertyInfo.GetValue(obj, null);
return propertyValue == null ? 0 : propertyValue.GetHashCode();
}
}
then, You can remove duplicate items in your list.
var products = new List<Product>
{
new Product{ProductName = "product 1" ,Id = 1,},
new Product{ProductName = "product 2" ,Id = 2,},
new Product{ProductName = "product 2" ,Id = 4,},
new Product{ProductName = "product 2" ,Id = 4,},
};
var productList = products.Distinct(new ItemEqualityComparer<Product>(nameof(Product.Id))).ToList();
var customers = new List<Customer>
{
new Customer{CustomerName = "Customer 1" ,Id = 5,},
new Customer{CustomerName = "Customer 2" ,Id = 5,},
new Customer{CustomerName = "Customer 2" ,Id = 5,},
new Customer{CustomerName = "Customer 2" ,Id = 5,},
};
var customerList = customers.Distinct(new ItemEqualityComparer<Customer>(nameof(Customer.Id))).ToList();
this code remove duplicate items by Id if you want remove duplicate items by other property, you can change nameof(YourClass.DuplicateProperty) same nameof(Customer.CustomerName) then remove duplicate items by CustomerName Property.
If you don't care about the order you can just shove the items into a HashSet, if you do want to maintain the order you can do something like this:
var unique = new List<T>();
var hs = new HashSet<T>();
foreach (T t in list)
if (hs.Add(t))
unique.Add(t);
Or the Linq way:
var hs = new HashSet<T>();
list.All( x => hs.Add(x) );
Edit: The HashSet method is O(N) time and O(N) space while sorting and then making unique (as suggested by #lassevk and others) is O(N*lgN) time and O(1) space so it's not so clear to me (as it was at first glance) that the sorting way is inferior
Might be easier to simply make sure that duplicates are not added to the list.
if(items.IndexOf(new_item) < 0)
items.add(new_item)
You can use Union
obj2 = obj1.Union(obj1).ToList();
Another way in .Net 2.0
static void Main(string[] args)
{
List<string> alpha = new List<string>();
for(char a = 'a'; a <= 'd'; a++)
{
alpha.Add(a.ToString());
alpha.Add(a.ToString());
}
Console.WriteLine("Data :");
alpha.ForEach(delegate(string t) { Console.WriteLine(t); });
alpha.ForEach(delegate (string v)
{
if (alpha.FindAll(delegate(string t) { return t == v; }).Count > 1)
alpha.Remove(v);
});
Console.WriteLine("Unique Result :");
alpha.ForEach(delegate(string t) { Console.WriteLine(t);});
Console.ReadKey();
}
There are many ways to solve - the duplicates issue in the List, below is one of them:
List<Container> containerList = LoadContainer();//Assume it has duplicates
List<Container> filteredList = new List<Container>();
foreach (var container in containerList)
{
Container duplicateContainer = containerList.Find(delegate(Container checkContainer)
{ return (checkContainer.UniqueId == container.UniqueId); });
//Assume 'UniqueId' is the property of the Container class on which u r making a search
if(!containerList.Contains(duplicateContainer) //Add object when not found in the new class object
{
filteredList.Add(container);
}
}
Cheers
Ravi Ganesan
Here's a simple solution that doesn't require any hard-to-read LINQ or any prior sorting of the list.
private static void CheckForDuplicateItems(List<string> items)
{
if (items == null ||
items.Count == 0)
return;
for (int outerIndex = 0; outerIndex < items.Count; outerIndex++)
{
for (int innerIndex = 0; innerIndex < items.Count; innerIndex++)
{
if (innerIndex == outerIndex) continue;
if (items[outerIndex].Equals(items[innerIndex]))
{
// Duplicate Found
}
}
}
}
David J.'s answer is a good method, no need for extra objects, sorting, etc. It can be improved on however:
for (int innerIndex = items.Count - 1; innerIndex > outerIndex ; innerIndex--)
So the outer loop goes top bottom for the entire list, but the inner loop goes bottom "until the outer loop position is reached".
The outer loop makes sure the entire list is processed, the inner loop finds the actual duplicates, those can only happen in the part that the outer loop hasn't processed yet.
Or if you don't want to do bottom up for the inner loop you could have the inner loop start at outerIndex + 1.
A simple intuitive implementation:
public static List<PointF> RemoveDuplicates(List<PointF> listPoints)
{
List<PointF> result = new List<PointF>();
for (int i = 0; i < listPoints.Count; i++)
{
if (!result.Contains(listPoints[i]))
result.Add(listPoints[i]);
}
return result;
}
All answers copy lists, or create a new list, or use slow functions, or are just painfully slow.
To my understanding, this is the fastest and cheapest method I know (also, backed by a very experienced programmer specialized on real-time physics optimization).
// Duplicates will be noticed after a sort O(nLogn)
list.Sort();
// Store the current and last items. Current item declaration is not really needed, and probably optimized by the compiler, but in case it's not...
int lastItem = -1;
int currItem = -1;
int size = list.Count;
// Store the index pointing to the last item we want to keep in the list
int last = size - 1;
// Travel the items from last to first O(n)
for (int i = last; i >= 0; --i)
{
currItem = list[i];
// If this item was the same as the previous one, we don't want it
if (currItem == lastItem)
{
// Overwrite last in current place. It is a swap but we don't need the last
list[i] = list[last];
// Reduce the last index, we don't want that one anymore
last--;
}
// A new item, we store it and continue
else
lastItem = currItem;
}
// We now have an unsorted list with the duplicates at the end.
// Remove the last items just once
list.RemoveRange(last + 1, size - last - 1);
// Sort again O(n logn)
list.Sort();
Final cost is:
nlogn + n + nlogn = n + 2nlogn = O(nlogn) which is pretty nice.
Note about RemoveRange:
Since we cannot set the count of the list and avoid using the Remove funcions, I don't know exactly the speed of this operation but I guess it is the fastest way.
Using HashSet this can be done easily.
List<int> listWithDuplicates = new List<int> { 1, 2, 1, 2, 3, 4, 5 };
HashSet<int> hashWithoutDuplicates = new HashSet<int> ( listWithDuplicates );
List<int> listWithoutDuplicates = hashWithoutDuplicates.ToList();
Using HashSet:
list = new HashSet<T>(list).ToList();
public static void RemoveDuplicates<T>(IList<T> list )
{
if (list == null)
{
return;
}
int i = 1;
while(i<list.Count)
{
int j = 0;
bool remove = false;
while (j < i && !remove)
{
if (list[i].Equals(list[j]))
{
remove = true;
}
j++;
}
if (remove)
{
list.RemoveAt(i);
}
else
{
i++;
}
}
}
If you need to compare complex objects, you will need to pass a Comparer object inside the Distinct() method.
private void GetDistinctItemList(List<MyListItem> _listWithDuplicates)
{
//It might be a good idea to create MyListItemComparer
//elsewhere and cache it for performance.
List<MyListItem> _listWithoutDuplicates = _listWithDuplicates.Distinct(new MyListItemComparer()).ToList();
//Choose the line below instead, if you have a situation where there is a chance to change the list while Distinct() is running.
//ToArray() is used to solve "Collection was modified; enumeration operation may not execute" error.
//List<MyListItem> _listWithoutDuplicates = _listWithDuplicates.ToArray().Distinct(new MyListItemComparer()).ToList();
return _listWithoutDuplicates;
}
Assuming you have 2 other classes like:
public class MyListItemComparer : IEqualityComparer<MyListItem>
{
public bool Equals(MyListItem x, MyListItem y)
{
return x != null
&& y != null
&& x.A == y.A
&& x.B.Equals(y.B);
&& x.C.ToString().Equals(y.C.ToString());
}
public int GetHashCode(MyListItem codeh)
{
return codeh.GetHashCode();
}
}
And:
public class MyListItem
{
public int A { get; }
public string B { get; }
public MyEnum C { get; }
public MyListItem(int a, string b, MyEnum c)
{
A = a;
B = b;
C = c;
}
}
I think the simplest way is:
Create a new list and add unique item.
Example:
class MyList{
int id;
string date;
string email;
}
List<MyList> ml = new Mylist();
ml.Add(new MyList(){
id = 1;
date = "2020/09/06";
email = "zarezadeh#gmailcom"
});
ml.Add(new MyList(){
id = 2;
date = "2020/09/01";
email = "zarezadeh#gmailcom"
});
List<MyList> New_ml = new Mylist();
foreach (var item in ml)
{
if (New_ml.Where(w => w.email == item.email).SingleOrDefault() == null)
{
New_ml.Add(new MyList()
{
id = item.id,
date = item.date,
email = item.email
});
}
}