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WindowLeft.cs
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WindowLeft.cs
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namespace SuperLinq.Async;
public static partial class AsyncSuperEnumerable
{
/// <summary>
/// Creates a left-aligned sliding window of a given size over the
/// source sequence.
/// </summary>
/// <typeparam name="TSource">
/// The type of the elements of <paramref name="source"/>.</typeparam>
/// <param name="source">
/// The sequence over which to create the sliding window.</param>
/// <param name="size">Size of the sliding window.</param>
/// <returns>A sequence representing each sliding window.</returns>
/// <remarks>
/// <para>
/// A window can contain fewer elements than <paramref name="size"/>,
/// especially as it slides over the end of the sequence.</para>
/// <para>
/// This operator uses deferred execution and streams its results.</para>
/// </remarks>
/// <example>
/// <code><![CDATA[
/// Console.WriteLine(
/// Enumerable
/// .Range(1, 5)
/// .WindowLeft(3)
/// .Select(w => "AVG(" + w.ToDelimitedString(",") + ") = " + w.Average())
/// .ToDelimitedString(Environment.NewLine));
///
/// // Output:
/// // AVG(1,2,3) = 2
/// // AVG(2,3,4) = 3
/// // AVG(3,4,5) = 4
/// // AVG(4,5) = 4.5
/// // AVG(5) = 5
/// ]]></code>
/// </example>
public static IAsyncEnumerable<IList<TSource>> WindowLeft<TSource>(this IAsyncEnumerable<TSource> source, int size)
{
ArgumentNullException.ThrowIfNull(source);
ArgumentOutOfRangeException.ThrowIfNegativeOrZero(size);
return Core(source, size);
static async IAsyncEnumerable<IList<TSource>> Core(
IAsyncEnumerable<TSource> source, int size,
[EnumeratorCancellation] CancellationToken cancellationToken = default)
{
await using var e = source.GetConfiguredAsyncEnumerator(cancellationToken);
if (!await e.MoveNextAsync())
yield break;
var window = new TSource[size];
window[0] = e.Current;
for (var i = 1; i < size; i++)
{
if (!await e.MoveNextAsync())
{
Array.Resize(ref window, i);
goto skipLoop;
}
window[i] = e.Current;
}
while (await e.MoveNextAsync())
{
var newWindow = new TSource[size];
window.AsSpan()[1..].CopyTo(newWindow);
newWindow[^1] = e.Current;
yield return window;
window = newWindow;
}
skipLoop:
while (window.Length > 1)
{
var newWindow = new TSource[window.Length - 1];
window.AsSpan()[1..].CopyTo(newWindow);
yield return window;
window = newWindow;
}
yield return window;
}
}
}