c# – Teafiles和茶馆图表库背后的架构？

我不确切知道TeaHouse解决方案背后的技术类型.但我也使用了一种方法来显示一组点,这些点位于来自TeaFile的大量数据的两个日期之间.

ZedGraph库有一个FilteredPointList对象,它执行自动数据点抽取.它包含一个SetBounds方法,允许您选择要显示的日期范围以及要显示的最大点数.通常,它对应于视图的实际宽度.

FilteredPointList (original source code)使用两个包含XY数据的double数组.通过使用TeaFile对象替换数组,将此类调整为TeaFilePointList很容易,将T视为包含DateTime和double属性的结构.

实施不是最佳的,但我是这样开始的.我稍后可能会更新此代码以包含TeaFile的MemoryMappedFile功能.这种方式会快得多.

public class TeaFilePointList : IPointList
{
    TeaFile<point> tf;

    private int _maxPts = -1;
    private int _minBoundIndex = -1;
    private int _maxBoundIndex = -1;

    struct point
    {
        public TeaTime.Time x;
        public double y;
    }

    public TeaFilePointList(DateTime[] x,double[] y)
    {
        tf = TeaFile<point>.Create(Path.GetRandomFileName() + ".tea");
        for (var i = 0; i < x.Length; i++)
            tf.Write(new point() { x = x[i],y = y[i] });
    }

    public void SetBounds(double min,double max,int maxPts)
    {
        _maxPts = maxPts;

        // find the index of the start and end of the bounded range

        var xmin = (DateTime)new XDate(min);
        var xmax = (DateTime)new XDate(max);

        int first = tf.BinarySearch(xmin,item => (DateTime)item.x);
        int last = tf.BinarySearch(xmax,item => (DateTime)item.x);

        // Make sure the bounded indices are legitimate
        // if BinarySearch() doesn't find the value,it returns the bitwise
        // complement of the index of the 1st element larger than the sought value

        if (first < 0)
        {
            if (first == -1)
                first = 0;
            else
                first = ~(first + 1);
        }

        if (last < 0)
            last = ~last;

        _minBoundIndex = first;
        _maxBoundIndex = last;
    }

    public int Count
    {
        get
        {
            int arraySize = (int)tf.Count;

            // Is the filter active?
            if (_minBoundIndex >= 0 && _maxBoundIndex >= 0 && _maxPts > 0)
            {
                // get the number of points within the filter bounds
                int boundSize = _maxBoundIndex - _minBoundIndex + 1;

                // limit the point count to the filter bounds
                if (boundSize < arraySize)
                    arraySize = boundSize;

                // limit the point count to the declared max points
                if (arraySize > _maxPts)
                    arraySize = _maxPts;
            }

            return arraySize;
        }
    }

    public PointPair this[int index]
    {
        get
        {
            if (_minBoundIndex >= 0 && _maxBoundIndex >= 0 && _maxPts >= 0)
            {
                // get number of points in bounded range
                int nPts = _maxBoundIndex - _minBoundIndex + 1;

                if (nPts > _maxPts)
                {
                    // if we're skipping points,then calculate the new index
                    index = _minBoundIndex + (int)((double)index * (double)nPts / (double)_maxPts);
                }
                else
                {
                    // otherwise,index is just offset by the start of the bounded range
                    index += _minBoundIndex;
                }
            }

            double xVal,yVal;
            if (index >= 0 && index < tf.Count)
                xVal = new XDate(tf.Items[index].x);
            else
                xVal = PointPair.Missing;

            if (index >= 0 && index < tf.Count)
                yVal = tf.Items[index].y;
            else
                yVal = PointPair.Missing;

            return new PointPair(xVal,yVal,PointPair.Missing,null);
        }
    }

    public object Clone()
    {
        throw new NotImplementedException(); // I'm lazy...
    }

    public void Close()
    {
        tf.Close();
        tf.Dispose();
        File.Delete(tf.Name);
    }
}

最难的部分是为TeaFile实现BinarySearch,使用DateTime快速搜索记录.我使用反编译器查看了Array.BinarySearch实现,并在下面编写了扩展：

public static int BinarySearch<T,U>(this TeaFile<T> tf,U target,Func<T,U> indexer) where T : struct
{
    var lo = 0;
    var hi = (int)tf.Count - 1;
    var comp = Comparer<U>.Default;

    while(lo <= hi)
    {
        var median = lo + (hi - lo >> 1);
        var num = comp.Compare(indexer(tf.Items[median]),target);
        if (num == 0)
            return median;
        if (num < 0)
            lo = median + 1;
        else
            hi = median - 1;
    }

    return ~lo;
}

如果ZedGraph不符合您的需求,至少您明白了. FilteredPointList类中使用的抽取算法非常好,可以通过其他方式进行调整以满足您的需求.