I have two arrays of ArrayList.
public class ProductDetails
{
public string id;
public string description;
public float rate;
}
ArrayList products1 = new ArrayList();
ArrayList products2 = new ArrayList();
ArrayList duplicateProducts = new ArrayList();
Now what I want is to get all the products (with all the fields of ProductDetails class) having duplicate description in both products1 and products2.
I can run two for/while loops as traditional way, but that would be very slow specially if I will be having over 10k elements in both arrays.
So probably something can be done with LINQ.
If you want to use linQ, you need write your own EqualityComparer where you override both methods Equals and GetHashCode()
public class ProductDetails
{
public string id {get; set;}
public string description {get; set;}
public float rate {get; set;}
}
public class ProductComparer : IEqualityComparer<ProductDetails>
{
public bool Equals(ProductDetails x, ProductDetails y)
{
//Check whether the objects are the same object.
if (Object.ReferenceEquals(x, y)) return true;
//Check whether the products' properties are equal.
return x != null && y != null && x.id.Equals(y.id) && x.description.Equals(y.description);
}
public int GetHashCode(ProductDetails obj)
{
//Get hash code for the description field if it is not null.
int hashProductDesc = obj.description == null ? 0 : obj.description.GetHashCode();
//Get hash code for the idfield.
int hashProductId = obj.id.GetHashCode();
//Calculate the hash code for the product.
return hashProductDesc ^ hashProductId ;
}
}
Now, supposing you have this objects:
ProductDetails [] items1= { new ProductDetails { description= "aa", id= 9, rating=2.0f },
new ProductDetails { description= "b", id= 4, rating=2.0f} };
ProductDetails [] items= { new ProductDetails { description= "aa", id= 9, rating=1.0f },
new ProductDetails { description= "c", id= 12, rating=2.0f } };
IEnumerable<ProductDetails> duplicates =
items1.Intersect(items2, new ProductComparer());
Consider overriding the System.Object.Equals method.
public class ProductDetails
{
public string id;
public string description;
public float rate;
public override bool Equals(object obj)
{
if(obj is ProductDetails == null)
return false;
if(ReferenceEquals(obj,this))
return true;
ProductDetails p = (ProductDetails)obj;
return description == p.description;
}
}
Filtering would then be as simple as:
var result = products1.Where(product=>products2.Contains(product));
EDIT:
Do consider that this implementation is not optimal..
Moreover- it has been proposed in the comments to your question that you use a data base.
This way performance will be optimized - as per the database implementation In any case- the overhead will not be yours.
However, you can optimize this code by using a Dictionary or a HashSet:
Overload the System.Object.GetHashCode method:
public override int GetHashCode()
{
return description.GetHashCode();
}
You can now do this:
var hashSet = new HashSet<ProductDetails>(products1);
var result = products2.Where(product=>hashSet.Contains(product));
Which will boost your performance to an extent since lookup will be less costly.
10k elements is nothing, however make sure you use proper collection types. ArrayList is long deprecated, use List<ProductDetails>.
Next step is implementing proper Equals and GetHashCode overrides for your class. The assumption here is that description is the key since that's what you care about from a duplication point of view:
public class ProductDetails
{
public string id;
public string description;
public float rate;
public override bool Equals(object obj)
{
var p = obj as ProductDetails;
return ReferenceEquals(p, null) ? false : description == obj.description;
}
public override int GetHashCode() => description.GetHashCode();
}
Now we have options. One easy and efficient way of doing this is using a hash set:
var set = new HashSet<ProductDetails>();
var products1 = new List<ProductDetails>(); // fill it
var products2 = new List<ProductDetails>(); // fill it
// shove everything in the first list in the set
foreach(var item in products1)
set.Add(item);
// and simply test the elements in the second set
foreach(var item in products2)
if(set.Contains(item))
{
// item.description was already used in products1, handle it here
}
This gives you linear (O(n)) time-complexity, best you can get.
I have a really simple program that creates a bunch of objects and iterates through them to set each object's Priority property.
static void Main(string[] args)
{
foreach (var obj in ObjectCreator.CreateObjectsWithPriorities())
Console.WriteLine(String.Format("Object #{0} has priority {1}",
obj.Id, obj.Priority));
}
class ObjectCreator
{
public static IEnumerable<ObjectWithPriority> CreateObjectsWithPriorities()
{
var objs = new[] { 1, 2, 3 }.Select(i => new ObjectWithPriority() { Id = i });
ApplyPriorities(objs);
return objs;
}
static void ApplyPriorities(IEnumerable<ObjectWithPriority> objs)
{
foreach (var obj in objs)
{
obj.Priority = obj.Id * 10;
Console.WriteLine(String.Format("Set priority of object #{0} to {1}", obj.Id, obj.Priority));
}
}
}
class ObjectWithPriority
{
public int Id { get; set; }
public int Priority { get; set; }
}
I'm expecting the IEnumerable in the Main method to contain objects with modified priorities. However, all of them have the default value 0.
Here is the log:
Set priority of object #1 to 10
Set priority of object #2 to 20
Set priority of object #3 to 30
Object #1 has priority 0
Object #2 has priority 0
Object #3 has priority 0
What is the reason for suche behavior and what should I change here in order to get my priorities working?
When you do this:
var objs = new[] { 1, 2, 3 }.Select(i => new ObjectWithPriority() { Id = i });
You're simply creating a lazily evaluated iterator, this doesn't allocate an array/list to store the ObjectWithPriorty you project. Each time you enumerate the iterator, it will iterate the values again and project an ObjectWithPriority for each iteration, but will discard them.
What you want to do is materialize the query before you pass it, so later you'll actually modifying the already allocated list/array. This can be achieved using Enumerable.ToList or Enumerable.ToArray:
public static IEnumerable<ObjectWithPriority> CreateObjectsWithPriorities()
{
var objs = new[] { 1, 2, 3 }.Select(i => new ObjectWithPriority() { Id = i })
.ToList();
ApplyPriorities(objs);
return objs;
}
You could additional use Enumerable.Range instead of allocating a fixed size array, which will lazily project the numbers as requested:
var objs = Enumerable.Range(1, 3).Select(i => new ObjectWithPriority { Id = i })
.ToList();
To better understand what is happening in your program, you should think of this expression
var objs = new[] { 1, 2, 3 }.Select(i => new ObjectWithPriority() { Id = i });
as a query, not as a sequence/list/collection of objects.
But it is obvious from your code that in this particular program you don't need a query. You need a collection that has a finite number of objects and that returns the same objects every time you loop through it using foreach.
So a decent thing to do would be to use ICollection<ObjectWithPriority> instead of IEnumerable<ObjectWithPriority>. This would better represent the program's logic and help avoid some mistakes/misinterpretations like the one you stumbled upon.
The code could be modified as follows:
public static ICollection<ObjectWithPriority> CreateObjectsWithPriorities()
{
IEnumerable<ObjectWithPriority> queryThatProducesObjectsWithPriorities = new[] { 1, 2, 3 }.Select(i => new ObjectWithPriority() { Id = i }); // just for clarification
ICollection<ObjectWithPriority> objectsWithPriorities = queryThatProducesObjectsWithPriorities.ToList();
ApplyPriorities(objectsWithPriorities);
return objectsWithPriorities;
}
static void ApplyPriorities(ICollection<ObjectWithPriority> objs)
{
foreach (var obj in objs)
{
obj.Priority = obj.Id * 10;
Console.WriteLine(String.Format("Set priority of object #{0} to {1}", obj.Id, obj.Priority));
}
}
In Addition to the Answer of Yuval Itzchakov:
If you want to lazy-load the priority of your objects you could:
Define your ApplyPriorities() Method just for one object and use it in the select-Method OR add a delegate to your ObjectWithPriority class wich calculates the Priority like shown in the code below:
class ObjectWithPriority
{
public int Id { get; set; }
private int? priority;
public int Priority {
get
{
return (priority.HasValue ? priority.Value : (priority = PriorityProvider(this)).Value);
}
set { priority = value; }
}
Func<ObjectWithPriority, int> PriorityProvider { get; set; }
public ObjectWithPriority(Func<ObjectWithPriority, int> priorityProvider = null)
{
PriorityProvider = priorityProvider ?? (obj => 10 * obj.Id);
}
}
I have a large file which, in essence contains data like:
Netherlands,Noord-holland,Amsterdam,FooStreet,1,...,...
Netherlands,Noord-holland,Amsterdam,FooStreet,2,...,...
Netherlands,Noord-holland,Amsterdam,FooStreet,3,...,...
Netherlands,Noord-holland,Amsterdam,FooStreet,4,...,...
Netherlands,Noord-holland,Amsterdam,FooStreet,5,...,...
Netherlands,Noord-holland,Amsterdam,BarRoad,1,...,...
Netherlands,Noord-holland,Amsterdam,BarRoad,2,...,...
Netherlands,Noord-holland,Amsterdam,BarRoad,3,...,...
Netherlands,Noord-holland,Amsterdam,BarRoad,4,...,...
Netherlands,Noord-holland,Amstelveen,BazDrive,1,...,...
Netherlands,Noord-holland,Amstelveen,BazDrive,2,...,...
Netherlands,Noord-holland,Amstelveen,BazDrive,3,...,...
Netherlands,Zuid-holland,Rotterdam,LoremAve,1,...,...
Netherlands,Zuid-holland,Rotterdam,LoremAve,2,...,...
Netherlands,Zuid-holland,Rotterdam,LoremAve,3,...,...
...
This is a multi-gigabyte file. I have a class that reads this file and exposes these lines (records) as an IEnumerable<MyObject>. This MyObject has several properties (Country,Province,City, ...) etc.
As you can see there is a LOT of duplication of data. I want to keep exposing the underlying data as an IEnumerable<MyObject>. However, some other class might (and probably will) make some hierarchical view/structure of this data like:
Netherlands
Noord-holland
Amsterdam
FooStreet [1, 2, 3, 4, 5]
BarRoad [1, 2, 3, 4]
...
Amstelveen
BazDrive [1, 2, 3]
...
...
Zuid-holland
Rotterdam
LoremAve [1, 2, 3]
...
...
...
...
When reading this file, I do, essentially, this:
foreach (line in myfile) {
fields = line.split(",");
yield return new MyObject {
Country = fields[0],
Province = fields[1],
City = fields[2],
Street = fields[3],
//...other fields
};
}
Now, to the actual question at hand: I could use string.Intern() to intern the Country, Province, City, and Street strings (those are the main 'vilains', the MyObject has several other properties not relevant to the question).
foreach (line in myfile) {
fields = line.split(",");
yield return new MyObject {
Country = string.Intern(fields[0]),
Province = string.Intern(fields[1]),
City = string.Intern(fields[2]),
Street = string.Intern(fields[3]),
//...other fields
};
}
This will save about 42% of memory (tested and measured) when holding the entire dataset in memory since all duplicate strings will be a reference to the same string. Also, when creating the hierarchical structure with a lot of LINQ's .ToDictionary() method the keys (Country, Province etc.) of the resp. dictionaries will be much more efficient.
However, one of the drawbacks (aside a slight loss of performance, which is not problem) of using string.Intern() is that the strings won't be garbage collected anymore. But when I'm done with my data I do want all that stuff garbage collected (eventually).
I could use a Dictionary<string, string> to 'intern' this data but I don't like the "overhead" of having a key and value where I am, actually, only interested in the key. I could set the value to null or the use the same string as value (which will result in the same reference in key and value). It's only a small price of a few bytes to pay, but it's still a price.
Something like a HashSet<string> makes more sense to me. However, I cannot get a reference to a string in the HashSet; I can see if the HashSet contains a specific string, but not get a reference to that specific instance of the located string in the HashSet. I could implement my own HashSet for this, but I am wondering what other solutions you kind StackOverflowers may come up with.
Requirements:
My "FileReader" class needs to keep exposing an IEnumerable<MyObject>
My "FileReader" class may do stuff (like string.Intern()) to optimize memory usage
The MyObject class cannot change; I won't make a City class, Country class etc. and have MyObject expose those as properties instead of simple string properties
Goal is to be (more) memory efficient by de-duplicating most of the duplicate strings in Country, Province, City etc.; how this is achieved (e.g. string interning, internal hashset / collection / structure of something) is not important. However:
I know I can stuff the data in a database or use other solutions in such direction; I am not interested in these kind of solutions.
Speed is only of secondary concern; the quicker the better ofcourse but a (slight) loss in performance while reading/iterating the objects is no problem
Since this is a long-running process (as in: windows service running 24/7/365) that, occasionally, processes a bulk of this data I want the data to be garbage-collected when I'm done with it; string interning works great but will, in the long run, result in a huge string pool with lots of unused data
I would like any solutions to be "simple"; adding 15 classes with P/Invokes and inline assembly (exaggerated) is not worth the effort. Code maintainability is high on my list.
This is more of a 'theoretical' question; it's purely out of curiosity / interest that I'm asking. There is no "real" problem, but I can see that in similar situations this might be a problem to someone.
For example: I could do something like this:
public class StringInterningObject
{
private HashSet<string> _items;
public StringInterningObject()
{
_items = new HashSet<string>();
}
public string Add(string value)
{
if (_items.Add(value))
return value; //New item added; return value since it wasn't in the HashSet
//MEH... this will quickly go O(n)
return _items.First(i => i.Equals(value)); //Find (and return) actual item from the HashSet and return it
}
}
But with a large set of (to be de-duplicated) strings this will quickly bog down. I could have a peek at the reference source for HashSet or Dictionary or... and build a similar class that doesn't return bool for the Add() method but the actual string found in the internals/bucket.
The best I could come up with until now is something like:
public class StringInterningObject
{
private ConcurrentDictionary<string, string> _items;
public StringInterningObject()
{
_items = new ConcurrentDictionary<string, string>();
}
public string Add(string value)
{
return _items.AddOrUpdate(value, value, (v, i) => i);
}
}
Which has the "penalty" of having a Key and a Value where I'm actually only interested in the Key. Just a few bytes though, small price to pay. Coincidally this also yields 42% less memory usage; the same result as when using string.Intern() yields.
tolanj came up with System.Xml.NameTable:
public class StringInterningObject
{
private System.Xml.NameTable nt = new System.Xml.NameTable();
public string Add(string value)
{
return nt.Add(value);
}
}
(I removed the lock and string.Empty check (the latter since the NameTable already does that))
xanatos came up with a CachingEqualityComparer:
public class StringInterningObject
{
private class CachingEqualityComparer<T> : IEqualityComparer<T> where T : class
{
public System.WeakReference X { get; private set; }
public System.WeakReference Y { get; private set; }
private readonly IEqualityComparer<T> Comparer;
public CachingEqualityComparer()
{
Comparer = EqualityComparer<T>.Default;
}
public CachingEqualityComparer(IEqualityComparer<T> comparer)
{
Comparer = comparer;
}
public bool Equals(T x, T y)
{
bool result = Comparer.Equals(x, y);
if (result)
{
X = new System.WeakReference(x);
Y = new System.WeakReference(y);
}
return result;
}
public int GetHashCode(T obj)
{
return Comparer.GetHashCode(obj);
}
public T Other(T one)
{
if (object.ReferenceEquals(one, null))
{
return null;
}
object x = X.Target;
object y = Y.Target;
if (x != null && y != null)
{
if (object.ReferenceEquals(one, x))
{
return (T)y;
}
else if (object.ReferenceEquals(one, y))
{
return (T)x;
}
}
return one;
}
}
private CachingEqualityComparer<string> _cmp;
private HashSet<string> _hs;
public StringInterningObject()
{
_cmp = new CachingEqualityComparer<string>();
_hs = new HashSet<string>(_cmp);
}
public string Add(string item)
{
if (!_hs.Add(item))
item = _cmp.Other(item);
return item;
}
}
(Modified slightly to "fit" my "Add() interface")
As per Henk Holterman's request:
public class StringInterningObject
{
private Dictionary<string, string> _items;
public StringInterningObject()
{
_items = new Dictionary<string, string>();
}
public string Add(string value)
{
string result;
if (!_items.TryGetValue(value, out result))
{
_items.Add(value, value);
return value;
}
return result;
}
}
I'm just wondering if there's maybe a neater/better/cooler way to 'solve' my (not so much of an actual) problem. By now I have enough options I guess
Here are some numbers I came up with for some simple, short, preliminary tests:
Non optimizedMemory: ~4,5GbLoad time: ~52s
StringInterningObject (see above, the ConcurrentDictionary variant)Memory: ~2,6GbLoad time: ~49s
string.Intern()Memory: ~2,3GbLoad time: ~45s
System.Xml.NameTableMemory: ~2,3GbLoad time: ~41s
CachingEqualityComparerMemory: ~2,3GbLoad time: ~58s
StringInterningObject (see above, the (non-concurrent) Dictionary variant) as per Henk Holterman's request:Memory: ~2,3GbLoad time: ~39s
Although the numbers aren't very definitive, it seems that the many memory-allocations for the non-optimized version actually slow down more than using either string.Intern() or the above StringInterningObjects which results in (slightly) longer load times. Also, string.Intern() seems to 'win' from StringInterningObject but not by a large margin; << See updates.
I've had exactly this requirement and indeed asked on SO, but with nothing like the detail of your question, no useful responses. One option that is built in is a (System.Xml).NameTable, which is basically a string atomization object, which is what you are looking for, we had (we've actually move to Intern because we do keep these strings for App-life).
if (name == null) return null;
if (name == "") return string.Empty;
lock (m_nameTable)
{
return m_nameTable.Add(name);
}
on a private NameTable
http://referencesource.microsoft.com/#System.Xml/System/Xml/NameTable.cs,c71b9d3a7bc2d2af shows its implemented as a Simple hashtable, ie only storing one reference per string.
Downside? is its completely string specific. If you do cross-test for memory / speed I'd be interested to see the results. We were already using System.Xml heavily, might of course not seem so natural if you where not.
When in doubt, cheat! :-)
public class CachingEqualityComparer<T> : IEqualityComparer<T> where T : class
{
public T X { get; private set; }
public T Y { get; private set; }
public IEqualityComparer<T> DefaultComparer = EqualityComparer<T>.Default;
public bool Equals(T x, T y)
{
bool result = DefaultComparer.Equals(x, y);
if (result)
{
X = x;
Y = y;
}
return result;
}
public int GetHashCode(T obj)
{
return DefaultComparer.GetHashCode(obj);
}
public T Other(T one)
{
if (object.ReferenceEquals(one, X))
{
return Y;
}
if (object.ReferenceEquals(one, Y))
{
return X;
}
throw new ArgumentException("one");
}
public void Reset()
{
X = default(T);
Y = default(T);
}
}
Example of use:
var comparer = new CachingEqualityComparer<string>();
var hs = new HashSet<string>(comparer);
string str = "Hello";
string st1 = str.Substring(2);
hs.Add(st1);
string st2 = str.Substring(2);
// st1 and st2 are distinct strings!
if (object.ReferenceEquals(st1, st2))
{
throw new Exception();
}
comparer.Reset();
if (hs.Contains(st2))
{
string cached = comparer.Other(st2);
Console.WriteLine("Found!");
// cached is st1
if (!object.ReferenceEquals(cached, st1))
{
throw new Exception();
}
}
I've created an equality comparer that "caches" the last Equal terms it analyzed :-)
Everything could then be encapsulated in a subclass of HashSet<T>
/// <summary>
/// An HashSet<T;gt; that, thorough a clever use of an internal
/// comparer, can have a AddOrGet and a TryGet
/// </summary>
/// <typeparam name="T"></typeparam>
public class HashSetEx<T> : HashSet<T> where T : class
{
public HashSetEx()
: base(new CachingEqualityComparer<T>())
{
}
public HashSetEx(IEqualityComparer<T> comparer)
: base(new CachingEqualityComparer<T>(comparer))
{
}
public T AddOrGet(T item)
{
if (!Add(item))
{
var comparer = (CachingEqualityComparer<T>)Comparer;
item = comparer.Other(item);
}
return item;
}
public bool TryGet(T item, out T item2)
{
if (Contains(item))
{
var comparer = (CachingEqualityComparer<T>)Comparer;
item2 = comparer.Other(item);
return true;
}
item2 = default(T);
return false;
}
private class CachingEqualityComparer<T> : IEqualityComparer<T> where T : class
{
public WeakReference X { get; private set; }
public WeakReference Y { get; private set; }
private readonly IEqualityComparer<T> Comparer;
public CachingEqualityComparer()
{
Comparer = EqualityComparer<T>.Default;
}
public CachingEqualityComparer(IEqualityComparer<T> comparer)
{
Comparer = comparer;
}
public bool Equals(T x, T y)
{
bool result = Comparer.Equals(x, y);
if (result)
{
X = new WeakReference(x);
Y = new WeakReference(y);
}
return result;
}
public int GetHashCode(T obj)
{
return Comparer.GetHashCode(obj);
}
public T Other(T one)
{
if (object.ReferenceEquals(one, null))
{
return null;
}
object x = X.Target;
object y = Y.Target;
if (x != null && y != null)
{
if (object.ReferenceEquals(one, x))
{
return (T)y;
}
else if (object.ReferenceEquals(one, y))
{
return (T)x;
}
}
return one;
}
}
}
Note the use of WeakReference so that there aren't useless references to objects that could prevent garbage collection.
Example of use:
var hs = new HashSetEx<string>();
string str = "Hello";
string st1 = str.Substring(2);
hs.Add(st1);
string st2 = str.Substring(2);
// st1 and st2 are distinct strings!
if (object.ReferenceEquals(st1, st2))
{
throw new Exception();
}
string stFinal = hs.AddOrGet(st2);
if (!object.ReferenceEquals(stFinal, st1))
{
throw new Exception();
}
string stFinal2;
bool result = hs.TryGet(st1, out stFinal2);
if (!object.ReferenceEquals(stFinal2, st1))
{
throw new Exception();
}
if (!result)
{
throw new Exception();
}
edit3:
instead of indexing strings, putting them in non-duplicate lists will save much more ram.
we have int indexes in class MyObjectOptimized. access is instant.
if list is short(like 1000 item) speed of setting values wont be noticable.
i assumed every string will have 5 character .
this will reduce memory usage
percentage : 110 byte /16byte = 9x gain
total : 5gb/9 = 0.7 gb + sizeof(Country_li , Province_li etc )
with int16 index (will further halve ram usage )
*note:* int16 capacity is -32768 to +32767 ,
make sure your list is not bigger than 32 767
usage is same but will use the class MyObjectOptimized
main()
{
// you can use same code
foreach (line in myfile) {
fields = line.split(",");
yield
return
new MyObjectOptimized {
Country = fields[0],
Province = fields[1],
City = fields[2],
Street = fields[3],
//...other fields
};
}
}
required classes
// single string size : 18 bytes (empty string size) + 2 bytes per char allocated
//1 class instance ram cost : 4 * (18 + 2* charCount )
// ie charcounts are at least 5
// cost: 4*(18+2*5) = 110 byte
class MyObject
{
string Country ;
string Province ;
string City ;
string Street ;
}
public static class Exts
{
public static int AddDistinct_and_GetIndex(this List<string> list ,string value)
{
if( !list.Contains(value) ) {
list.Add(value);
}
return list.IndexOf(value);
}
}
// 1 class instance ram cost : 4*4 byte = 16 byte
class MyObjectOptimized
{
//those int's could be int16 depends on your distinct item counts
int Country_index ;
int Province_index ;
int City_index ;
int Street_index ;
// manuallly implemented properties will not increase memory size
// whereas field WILL increase
public string Country{
get {return Country_li[Country_index]; }
set { Country_index = Country_li.AddDistinct_and_GetIndex(value); }
}
public string Province{
get {return Province_li[Province_index]; }
set { Province_index = Province_li.AddDistinct_and_GetIndex(value); }
}
public string City{
get {return City_li[City_index]; }
set { City_index = City_li.AddDistinct_and_GetIndex(value); }
}
public string Street{
get {return Street_li[Street_index]; }
set { Street_index = Street_li.AddDistinct_and_GetIndex(value); }
}
//beware they are static.
static List<string> Country_li ;
static List<string> Province_li ;
static List<string> City_li ;
static List<string> Street_li ;
}
I seem to be having some trouble wrapping my head around the idea of a Generic List of Generic Lists in C#. I think the problem stems form the use of the <T> argument, which I have no prior experience playing with. Could someone provide a short example of declaring a class which is a List, that therein contains another List, but where the type of the object contained therein is not immediately known?
I've been reading through the MS documentation on Generics, and I am not immediately sure if I can declare a List<List<T>>, nor how exactly to pass the <T> parameter to the inside list.
Edit: Adding information
Would declaring a List<List<T>> be considered legal here? In case you are wondering, I am building a class that allows me to use a ulong as the indexer, and (hopefully) steps around the nasty 2GB limit of .Net by maintaining a List of Lists.
public class DynamicList64<T>
{
private List<List<T>> data = new List<List<T>>();
private ulong capacity = 0;
private const int maxnumberOfItemsPerList = Int32.MaxValue;
public DynamicList64()
{
data = new List<List<T>>();
}
A quick example:
List<List<string>> myList = new List<List<string>>();
myList.Add(new List<string> { "a", "b" });
myList.Add(new List<string> { "c", "d", "e" });
myList.Add(new List<string> { "qwerty", "asdf", "zxcv" });
myList.Add(new List<string> { "a", "b" });
// To iterate over it.
foreach (List<string> subList in myList)
{
foreach (string item in subList)
{
Console.WriteLine(item);
}
}
Is that what you were looking for? Or are you trying to create a new class that extends List<T> that has a member that is a `List'?
or this example, just to make it more visible:
public class CustomerListList : List<CustomerList> { }
public class CustomerList : List<Customer> { }
public class Customer
{
public int ID { get; set; }
public string SomethingWithText { get; set; }
}
and you can keep it going. to the infinity and beyond !
A list of lists would essentially represent a tree structure, where each branch would constitute the same type as its parent, and its leaf nodes would represent values.
Implementation
public sealed class TreeList<T> : List<TreeList<T>>
{
public List<T> Values { get; } = new List<T>();
public TreeList<T> this[int index]
{
get
{
while (index > Count - 1)
{
Branch();
}
return base[index];
}
}
public TreeList<T> Branch()
{
TreeList<T> result = new TreeList<T>();
Add(result);
return result;
}
}
Example
internal static class Program
{
public static void Main()
{
// Create the root element...
TreeList<string> treeList = new TreeList<string>();
// You can add branches the old-fashioned way...
treeList.Add(new TreeList<string>());
// Add leaf node values to your first branch...
treeList[0].Values.Add("Hello, World!");
treeList[0].Values.Add("Goodbye, World!");
// You can create new branches from any branch like this...
// Note: You could also chain branch statements; i.e. treeList.Branch().Branch().Branch()
TreeList<string> branch2 = treeList.Branch();
// Add leaf node values to your second branch...
branch2.Values.Add("Alice");
branch2.Values.Add("Bob");
// You can also create branches until you reach the desired branch index...
// The TreeList indexer will loop until the desired index has been created, and then return it.
treeList[7].Values.Add("Alpha");
treeList[7].Values.Add("Bravo");
treeList[7].Values.Add("Charlie");
// How many branches does the root have?
Console.WriteLine($"Treelist branches: {treeList.Count}");
// What's at branch 0's values?
foreach (string value in treeList[0].Values)
{
Console.WriteLine(value);
}
// What's at branch 1's values?
foreach (string value in treeList[1].Values)
{
Console.WriteLine(value);
}
// What's at branch 7's values?
foreach (string value in treeList[7].Values)
{
Console.WriteLine(value);
}
}
}
Now, whether you should implement something like this is another matter. Extending List<T> isn't recommended: Why not inherit from List<T>?
public class ListOfLists<T> : List<List<T>>
{
}
var myList = new ListOfLists<string>();
I have the following code
public class ChildClass
{
public string FieldName { get; set; }
public string Value { get; set; }
public string StatusClass { get; set; }
public string StatusMessage { get; set; }
}
Creating a list of list obj is as follows
List<List<ChildClass>> obj = new List<List<ChildClass>>();
Look a direct example here:
public partial class Form1 : Form
{
List<List<Label>> txtList;
List<List<int>> num;
public Form1()
{
InitializeComponent();
txtList = new List< List<Label> >() {
new List<Label> { label1, label2, label3 },
new List<Label> { label4, label5, label6 },
new List<Label> { label7, label8, label9 }
};
num = new List<List<int>>() { new List<int>() { 1, 2 }, new List<int>() { 3, 4 } };
}
}
you should not use Nested List in List.
List<List<T>>
is not legal, even if T were a defined type.
https://msdn.microsoft.com/en-us/library/ms182144.aspx