Question

我正在寻找将数组拆分成固定大小的块的最快方法（当然，最后一个可以更小）。我在整个网站上看过并没有找到任何性能方面的比较，所以我写了它们，结果如下：

以微秒为单位的时间，平均值/错误/ stddev

int[] - 30.02 | 0.1002 | 0.0937

IEnumerable<int> - 76.67 | 0.2146 | 0.1902

更新：以下版本（在@Markus的回答中）为139.5 | 0.6702 | 0.5597

最流行的SO和经常推荐的使用LINQ的GroupBy和index/chunkSize的方法是不行的 - 267微秒比上述任何一种实现都要大得多。

有没有更快的方法来拆分数组？

P.S。这是Array和IEnumerable<T>的代码：

    /// <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;
        }
    }

P.P.S使用BenchmarkDotNet测试的完整解决方案为on GitHub。

Answer 1

不确定这是如何叠加的（ArraySegment），但试一试。我已经避免使用迭代器，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;
}

Answer 2

我使用了此代码：

来源：http://blogs.msdn.com/b/pfxteam/archive/2012/11/16/plinq-and-int32-maxvalue.aspx

public static IEnumerable<IEnumerable<T>> Batch<T>(this IEnumerable<T> source, int batchSize) {
    if (batchSize <= 0) {
        throw new ArgumentOutOfRangeException(nameof(batchSize));
    }
    using(var enumerator = source.GetEnumerator()) {
        while (enumerator.MoveNext()) {
            yield return YieldBatchElements(enumerator, batchSize - 1);
        }
    }
}

private static IEnumerable<T> YieldBatchElements<T>(IEnumerator<T> source, int batchSize) {
    yield return source.Current;
    for (var i = 0; i < batchSize && source.MoveNext(); i++) {
        yield return source.Current;
    }
}

Answer 3

您可以使用这几行代码

                int chunkSize = 4;
                int skipIndex = 0;
                string[] words = { "one", "two", "three", "four", "five", "six" };
                string[][] chunckResult = new string[words.Length][];

                for (int index = 0; index < words.Length; index++)
                {
                    chunckResult[index] = words.Skip(skipIndex).Take(chunkSize).ToArray();
                    skipIndex += chunkSize;
                    if (skipIndex == words.Length)
                    {
                        break;
                    }
                }

将数组拆分成块 - 有更快的方法吗？

3 个答案: