Indices and ranges C#

Indices and ranges provide a succinct syntax for accessing single elements or ranges in a sequence. Indexes and ranges provide clear, concise syntax to access a single element or a range of elements in a sequence. An index expression typically returns the type of the elements of a sequence.

The 0 index is the same as sequence[0]. The ^0 index is the same as sequence[sequence.Length]. The expression sequence[^0] throws an exception, just as sequence[sequence.Length] does. 

string[] words = [
                // index from start    index from end
    "The",      // 0                   ^9
    "quick",    // 1                   ^8
    "brown",    // 2                   ^7
    "fox",      // 3                   ^6
    "jumps",    // 4                   ^5
    "over",     // 5                   ^4
    "the",      // 6                   ^3
    "lazy",     // 7                   ^2
    "dog"       // 8                   ^1
];              // 9 (or words.Length) ^0

 

Examples:

string[] quickBrownFox = words[1..4]; // The range with the words "quick", "brown" и "fox"
string[] lazyDog = words[^2..^0]; // The range with the words "lazy" and "dog"
string[] allWords = words[..]; // contains "The" through "dog".
string[] firstPhrase = words[..4]; // contains "The" through "fox"
string[] lastPhrase = words[6..]; // contains "the", "lazy" and "dog"

 

You can also declare ranges or indices as variables. The variable can then be used inside the [ and ] characters:

Index the = ^3;
Console.WriteLine(words[the]);
Range phrase = 1..4;
string[] text = words[phrase];
foreach (var word in text)
    Console.Write($"< {word} >");

 

Scenarios for indices and ranges

You'll often use ranges and indices when you want to analyze a portion of a larger sequence. The new syntax is clearer in reading exactly what portion of the sequence is involved. The local function MovingAverage takes a Range as its argument. The method then enumerates just that range when calculating the min, max, and average.

int[] sequence = Sequence(1000);

for(int start = 0; start < sequence.Length; start += 100)
{
    Range r = start..(start+10);
    var (min, max, average) = MovingAverage(sequence, r);
    Console.WriteLine($"From {r.Start} to {r.End}:    \tMin: {min},\tMax: {max},\tAverage: {average}");
}

for (int start = 0; start < sequence.Length; start += 100)
{
    Range r = ^(start + 10)..^start;
    var (min, max, average) = MovingAverage(sequence, r);
    Console.WriteLine($"From {r.Start} to {r.End}:  \tMin: {min},\tMax: {max},\tAverage: {average}");
}

(int min, int max, double average) MovingAverage(int[] subSequence, Range range) =>
    (
        subSequence[range].Min(),
        subSequence[range].Max(),
        subSequence[range].Average()
    );

int[] Sequence(int count) => [..Enumerable.Range(0, count).Select(x => (int)(Math.Sqrt(x) * 100))];

 

Source: https://learn.microsoft.com/dotnet/csharp/tutorials/ranges-indexes

 

Archives