CSharp Itertools

This library implements a number of iterator building blocks inspired by Python 3 itertools module. Each has been recast in a form suitable for C#.

Installation

You can either register Itertools class in DI (Dependency Injection)

services.AddItertools();

... or instantiate manually.

IItertools itertools = new Itertools();

Infinite iterators

Cycle:

using CSharpItertools;

var itertools = new Itertools();

foreach (char letter in itertools.Cycle("ABCD"))
    Console.WriteLine(letter);

Output:

A
B
C
D
A
B
... // repeats indefinitely

Iterators terminating on the shortest input sequence

Zip and ZipLongest:

Make an iterator that aggregates elements from each of the iterables.

using CSharpItertools;

var itertools = new Itertools();

var iterable1 = new[] { 1, 2, 3 };
var iterable2 = new[] { 'A', 'B', 'C', 'D' };

forech (var item in itertools.Zip(iterable1, iterable2))
    Console.WriteLine(item);
  
forech (var item in itertools.ZipLongest(iterable1, iterable2))
    Console.WriteLine(item);

Output Zip:

(1, A)
(2, B)
(3, C)

Output ZipLongest:

• If the iterables are of uneven length, missing values are filled-in with null. Iteration continues until the longest iterable is exhausted.

(1, A)
(2, B)
(3, C)
(, D)

FilterFalse:

Make an iterator that filters elements from iterable returning only those for which the predicate is false.

using CSharpItertools;

var itertools = new Itertools();
var iterable = new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };

foreach (int i in itertools.FilterFalse(x => x % 2 > 0, iterable))
    Console.WriteLine(i);

Output:

2
4
6
8

ISlice

Make an iterator that returns selected elements from the iterable.

using CSharpItertools;

var itertools = new Itertools();
var iterable = new[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I' };

foreach (char l in itertools.ISlice(iterable, start: 3, stop: 6))
    Console.WriteLine(l);

Output:

D
E
F

Compress

Make an iterator that filters elements from data returning only those that have a corresponding element in selectors that evaluates to true.

using CSharpItertools;

var itertools = new Itertools();

var iterable = new[] { 'X', 'Y', 'Z', 'W' };
var selectors = new object[] { true, false, true, null };

foreach (char l in itertools.Compress(iterable, selectors))
    Console.WriteLine(l);

Output:

X
Z

Combinatoric iterators

Product

Cartesian product of input iterables.

using CSharpItertools;

var itertools = new Itertools();

var iterable1 = new List<int> { 1, 2, 3 };
var iterable2 = new List<int> { 6, 7 };

foreach (var arr in itertools.Product(iterable1, iterable2))
    Console.WriteLine("[{0}, {1}]", arr[0], arr[1]); // Output 1
    
var iterable3 = new[] { 'X', 'Y', 'Z' };

foreach (var arr in itertools.Product(iterable3, repeat: 2))
    Console.WriteLine("[{0}, {1}]", arr[0], arr[1]); // Output 2

Output 1:

[1, 6]
[1, 7]
[2, 6]
[2, 7]
[3, 6]
[3, 7]

Output 2:

[X, X]
[X, Y]
[X, Z]
[Y, X]
[Y, Y]
[Y, Z]
[Z, X]
[Z, Y]
[Z, Z]

Permutations

Return successive r length permutations of elements in the iterable.

using CSharpItertools;

var itertools = new Itertools();
var iterable = "ABCD";

foreach (var arr in itertools.Permutations(iterable, 2))
    Console.WriteLine("[{0}, {1}]", arr[0], arr[1]);

Output:

[A, B]
[A, C]
[A, D]
[B, A]
[B, C]
[B, D]
[C, A]
[C, B]
[C, D]
[D, A]
[D, B]
[D, C]

Combinations

Return r length subsequences of elements from the input iterable.

using CSharpItertools;

var itertools = new Itertools();
var iterable = new object[] { 'A', 3, 9, 'Z' };

foreach (object[] arr in itertools.Combinations(iterable, 3))
    Console.WriteLine("[{0}, {1}, {2}]", arr[0], arr[1], arr[2]);

Output:

[A, 3, 9]
[A, 3, Z]
[A, 9, Z]
[3, 9, Z]