https://github.com/netfabric/netfabric.doublylinkedlist
An alternative to LinkedList<T> with reverse operation and enumeration without allocation.
https://github.com/netfabric/netfabric.doublylinkedlist
csharp csharp-library dotnet dotnet-library dotnet-standard doubly-linked-list doublylinkedlist enumeration nuget-package sourcelink
Last synced: 8 months ago
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An alternative to LinkedList<T> with reverse operation and enumeration without allocation.
- Host: GitHub
- URL: https://github.com/netfabric/netfabric.doublylinkedlist
- Owner: NetFabric
- License: mit
- Created: 2018-11-28T20:58:27.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2023-09-10T20:30:12.000Z (almost 3 years ago)
- Last Synced: 2025-03-25T23:24:14.184Z (about 1 year ago)
- Topics: csharp, csharp-library, dotnet, dotnet-library, dotnet-standard, doubly-linked-list, doublylinkedlist, enumeration, nuget-package, sourcelink
- Language: C#
- Size: 152 KB
- Stars: 17
- Watchers: 1
- Forks: 4
- Open Issues: 7
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# NetFabric.DoublyLinkedList
[](https://github.com/NetFabric/NetFabric.DoublyLinkedList/actions/workflows/dotnet.yml)
[](https://coveralls.io/github/NetFabric/NetFabric.DoublyLinkedList)
[](https://www.nuget.org/packages/NetFabric.DoublyLinkedList/)
[](https://www.nuget.org/packages/NetFabric.DoublyLinkedList/)
An alternative to the [`System.Collections.Generic.LinkedList`](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.linkedlist-1) with reverse operation and enumeration without allocation.
The public API is very similar but the internals are very different with a more efficient implementation.
New overrides and methods were added to minimizing the memory allocations, number of loops, conditions and assignments required in multiple scenarios.
## Benchmarks
Performance comparison between [`System.Collections.Generic.LinkedList`](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.linkedlist-1) and `DoublyLinkedList`.
The benchmarks project is part of the repository. You can check the code and run it on your machine.
### Constructor performance
| Method | Count | Mean | Error | StdDev | Median | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|------------------------------- |------ |-------------:|-----------:|-----------:|-------------:|------:|--------:|-------:|------:|------:|----------:|
| **LinkedList_Enumerable** | **0** | **12.082 ns** | **0.3174 ns** | **0.4942 ns** | **12.091 ns** | **1.00** | **0.00** | **0.0191** | **-** | **-** | **40 B** |
| LinkedList_List | 0 | 21.542 ns | 0.9611 ns | 2.7884 ns | 19.863 ns | 2.07 | 0.21 | 0.0382 | - | - | 80 B |
| DoublyLinkedList_Enumerable | 0 | 10.749 ns | 0.0741 ns | 0.0657 ns | 10.761 ns | 0.89 | 0.04 | 0.0191 | - | - | 40 B |
| DoublyLinkedList_List | 0 | 7.533 ns | 0.1320 ns | 0.1170 ns | 7.511 ns | 0.62 | 0.03 | 0.0191 | - | - | 40 B |
| DoublyLinkedList_List_Reversed | 0 | 7.391 ns | 0.1275 ns | 0.1192 ns | 7.386 ns | 0.61 | 0.03 | 0.0191 | - | - | 40 B |
| | | | | | | | | | | | |
| **LinkedList_Enumerable** | **10** | **205.166 ns** | **1.2539 ns** | **1.1116 ns** | **205.147 ns** | **1.00** | **0.00** | **0.2677** | **-** | **-** | **560 B** |
| LinkedList_List | 10 | 241.563 ns | 1.7717 ns | 2.3651 ns | 241.213 ns | 1.18 | 0.01 | 0.2675 | - | - | 560 B |
| DoublyLinkedList_Enumerable | 10 | 163.873 ns | 1.8013 ns | 1.5042 ns | 163.424 ns | 0.80 | 0.01 | 0.2677 | - | - | 560 B |
| DoublyLinkedList_List | 10 | 142.060 ns | 1.3490 ns | 1.1265 ns | 142.538 ns | 0.69 | 0.01 | 0.2487 | - | - | 520 B |
| DoublyLinkedList_List_Reversed | 10 | 139.378 ns | 1.0579 ns | 0.8834 ns | 139.184 ns | 0.68 | 0.00 | 0.2487 | - | - | 520 B |
| | | | | | | | | | | | |
| **LinkedList_Enumerable** | **100** | **1,804.348 ns** | **16.3064 ns** | **15.2530 ns** | **1,808.247 ns** | **1.00** | **0.00** | **2.3327** | **-** | **-** | **4,880 B** |
| LinkedList_List | 100 | 1,894.060 ns | 12.0334 ns | 11.2561 ns | 1,895.876 ns | 1.05 | 0.01 | 2.3327 | - | - | 4,880 B |
| DoublyLinkedList_Enumerable | 100 | 1,355.031 ns | 16.9081 ns | 14.1191 ns | 1,352.691 ns | 0.75 | 0.01 | 2.3327 | - | - | 4,880 B |
| DoublyLinkedList_List | 100 | 1,216.764 ns | 11.3984 ns | 10.6620 ns | 1,218.606 ns | 0.67 | 0.01 | 2.3136 | - | - | 4,840 B |
| DoublyLinkedList_List_Reversed | 100 | 1,233.906 ns | 11.7235 ns | 10.9662 ns | 1,238.096 ns | 0.68 | 0.01 | 2.3136 | - | - | 4,840 B |
### Enumeration performance
| Method | Categories | Count | Mean | Error | StdDev | Ratio | RatioSD | Gen 0 | Gen 1 | Gen 2 | Allocated |
|--------------------------------- |----------- |------- |---------:|--------:|--------:|------:|--------:|--------:|--------:|--------:|----------:|
| LinkedList_Forward_While | Forward | 100000 | 320.0 μs | 3.77 μs | 3.53 μs | 1.00 | 0.00 | - | - | - | - |
| LinkedList_Forward_ForEach | Forward | 100000 | 496.1 μs | 5.55 μs | 5.19 μs | 1.55 | 0.02 | - | - | - | - |
| DoublyLinkedList_Forward_While | Forward | 100000 | 306.3 μs | 3.37 μs | 3.15 μs | 0.96 | 0.01 | - | - | - | - |
| DoublyLinkedList_Forward_ForEach | Forward | 100000 | 470.0 μs | 4.44 μs | 3.70 μs | 1.47 | 0.01 | - | - | - | - |
| | | | | | | | | | | | |
| LinkedList_Reverse_While | Reverse | 100000 | 353.5 μs | 6.03 μs | 5.03 μs | 1.00 | 0.00 | - | - | - | - |
| LinkedList_Reverse_ForEach | Reverse | 100000 | 934.6 μs | 7.46 μs | 6.23 μs | 2.64 | 0.04 | 41.0156 | 41.0156 | 41.0156 | 400,393 B |
| DoublyLinkedList_Reverse_While | Reverse | 100000 | 356.4 μs | 2.89 μs | 2.70 μs | 1.01 | 0.02 | - | - | - | - |
| DoublyLinkedList_Reverse_ForEach | Reverse | 100000 | 499.3 μs | 6.13 μs | 5.44 μs | 1.42 | 0.03 | - | - | - | - |
## Forward and reverse enumeration
`DoublyLinkedList` does not directly implement `IEnumerable`. Call the properties `Forward` or `Backward` to get an enumerator that goes in the direction you require.
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
foreach (var item in list.Backward)
Console.Write(item);
```
outputs
```
4321
```
These methods allow the use of LINQ on either direction:
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
Console.Write(list.Backward.First());
```
outputs
```
4
```
Although these enumerators are optimized for performance, they perform a bit more method calls and conditions than simply using a `while` loop to go throught the `Node` references. The performance penalty can be seen on the benchmarks above.
```csharp
var current = doublyLinkedList.Last;
while (current is object)
{
Console.Write(current.Value);
current = current.Previous;
}
```
The enumerators also supports random access by using an indexer. It allows indexing relative to the head or the tail of the list.
```csharp
var head = doublyLinkedList.Forward[0];
var tail = doublyLinkedList.Backward[0];
```
Please note that this `DoublyLinkedList` is not optimized for random access. It will use the shortest path to the item but it will have to step through the list to get there.
## `AddFirst()` and `AddLast()`
These methods now support the addition of collections of items. These can come from an `IEnumerable`, `IReadOnlyList` or another `DoublyLinkedList`.
When the parameter is `IReadOnlyList` or `DoublyLinkedList`, they can be added reversed.
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
var anotherList = new DoublyLinkedList(new[] {5, 6, 7, 8});
list.AddFirst(anotherList, true);
foreach (var item in list.Forward)
Console.Write(item);
```
outputs
```csharp
87651234
```
## `AddFirstFrom()` and `AddLastFrom()`
These methods perform the addition of a `DoublyLinkedList` but moving the nodes into the other `DoublyLinkedList`. No memory allocations and copies of values are performed.
The `DoublyLinkedList` passed as parameter becomes empty.
## `Append()`
A static method that returns a `DoublyLinkedList` instance with the items of both lists appended.
```csharp
var list = DoublyLinkedList.Append(
new DoublyLinkedList(new[] {1, 2, 3, 4}),
new DoublyLinkedList(new[] {5, 6, 7, 8}));
foreach (var item in list.Forward)
Console.Write(item);
```
outputs
```
12345678
```
## `Clone()`
Returns a shallow clone of the a `DoublyLinkedList`.
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
var clone = list.Clone();
foreach (var item in list.Forward)
Console.Write(item);
```
outputs
```
1234
```
## `Reverse()`
Returns a shallow clone of the a `DoublyLinkedList` with the items in reversed order.
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
var reversed = list.Reverse();
foreach (var item in reversed.Forward)
Console.Write(item);
```
outputs
```
4321
```
## `ReverseInPlace()`
`ReverseInPlace()` reverses the list items in-place. It flips the internal node references with no memory allocations.
```csharp
var list = new DoublyLinkedList(new[] {1, 2, 3, 4});
list.ReverseInPlace();
foreach (var item in list.Forward)
Console.Write(item);
```
also outputs
```
4321
```
##