Range Operator (..)

The .. operator specifies the start and end of a range of indices as its operands. The range operator is used to specify the start and end of a range for a sequence.

var people = new string[] { "Jane", "Jean", "Grey", "Marcus", "Theophilus", "Keje" };
var all = people[..];           // contains all elements
var firstFour = people[..4];    // contains the first four elements
var lastTwo = people[4..];      // contains "Theophilus" and "Keje"

The following table shows various ways to express collection ranges:

Range operator expression	Description
..	All values in the collection.
..end	Values from the start to the end exclusively.
start..	Values from the start to the end inclusively.
start..end	Values from the start inclusively to the end exclusively.
^start..	Values from the start inclusively to the end counting from the end.
..^end	Values from the start to the end exclusively counting from the end.
start..^end	Values from start inclusively to end exclusively counting from the end.
^start..^end	Values from start inclusively to end exclusively both counting from the end.

The following example demonstrates the effect of using all the ranges presented in the preceding table:

int[] oneThroughTen = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

Write(oneThroughTen, ..);
Write(oneThroughTen, ..3);
Write(oneThroughTen, 2..);
Write(oneThroughTen, 3..5);
Write(oneThroughTen, ^2..);
Write(oneThroughTen, ..^3);
Write(oneThroughTen, 3..^4);
Write(oneThroughTen, ^4..^2);

static void Write(int[] values, Range range) =>
    Console.WriteLine($"{range}:\t{string.Join(", ", values[range])}");
// Sample output:
//      0..^0:      1, 2, 3, 4, 5, 6, 7, 8, 9, 10
//      0..3:       1, 2, 3
//      2..^0:      3, 4, 5, 6, 7, 8, 9, 10
//      3..5:       4, 5
//      ^2..^0:     9, 10
//      0..^3:      1, 2, 3, 4, 5, 6, 7
//      3..^4:      4, 5, 6
//      ^4..^2:     7, 8