c# - 将数组拆分成 block - 有更快的方法吗？

Question

我正在寻找将数组拆分为固定大小块的最快方法(当然，最后一个可以更小)。我查看了整个网站，没有找到任何性能方面的比较，所以我写了它们，结果如下:

Time in microseconds, mean/error/stddev

For int[] - 30.02 | 0.1002 | 0.0937

For IEnumerable<int> - 76.67 | 0.2146 | 0.1902

更新:下面的版本(在@Markus 的回答中)是 139.5 | 0.6702 | 0.5597

在 SO 上最流行和经常推荐的使用 LINQ 的方法 GroupBy与 index/chunkSize是不行的 - 267 微秒比上述任何一个实现都大得多。

有没有更快的拆分数组的方法？

附言这是 Array 的代码和 IEnumerable<T> :

    /// <summary>
    /// Splits <paramref name="source"/> into chunks of size not greater than <paramref name="chunkMaxSize"/>
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="source">Array to be split</param>
    /// <param name="chunkMaxSize">Max size of chunk</param>
    /// <returns><see cref="IEnumerable{T}"/> of <see cref="Array"/> of <typeparam name="T"/></returns>
    public static IEnumerable<T[]> AsChunks<T>(this T[] source, int chunkMaxSize)
    {
        var pos = 0;
        var sourceLength = source.Length;
        do
        {
            var len = Math.Min(pos + chunkMaxSize, sourceLength) - pos;
            if (len == 0)
            {
                yield break;;
            }
            var arr = new T[len];
            Array.Copy(source, pos, arr, 0, len);
            pos += len;
            yield return arr;
        } while (pos < sourceLength);
    }

    /// <summary>
    /// Splits <paramref name="source"/> into chunks of size not greater than <paramref name="chunkMaxSize"/>
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="source"><see cref="IEnumerable{T}"/> to be split</param>
    /// <param name="chunkMaxSize">Max size of chunk</param>
    /// <returns><see cref="IEnumerable{T}"/> of <see cref="Array"/> of <typeparam name="T"/></returns>
    public static IEnumerable<T[]> AsChunks<T>(this IEnumerable<T> source, int chunkMaxSize)
    {
        var arr = new T[chunkMaxSize];
        var pos = 0;
        foreach (var item in source)
        {
            arr[pos++] = item;
            if (pos == chunkMaxSize)
            {
                yield return arr;
                arr = new T[chunkMaxSize];
                pos = 0;
            }
        }
        if (pos > 0)
        {
            Array.Resize(ref arr, pos);
            yield return arr;
        }
    }

带有 BenchmarkDotNet 测试的 P.P.S 完整解决方案是 on GitHub .

Answer 1

不太确定这是如何叠加的 (ArraySegment)，但请尝试一下。我避免使用迭代器，但不确定这是否真的是一个收获。

public static IEnumerable<T[]> AsChunks<T>(
    this T[] source, int chunkMaxSize)
{
    var chunks = source.Length / chunkMaxSize;
    var leftOver = source.Length % chunkMaxSize;
    var result = new List<T[]>(chunks + 1);
    var offset = 0;

    for (var i = 0; i < chunks; i++)
    {
        result.Add(new ArraySegment<T>(source,
                                       offset, 
                                       chunkMaxSize).ToArray());
        offset += chunkMaxSize;
    }

    if (leftOver > 0)
    {
        result.Add(new ArraySegment<T>(source, 
                                       offset, 
                                       leftOver).ToArray());
    }

    return result;
}