我对C＃不太熟悉。如何循环遍历数据表以分别计算每个类的前四列？

问题描述

我发现的所有示例都使用foreach循环。在添加其他2个类之前，我使用了foreach循环，但现在我必须使索引工作正常。有什么建议吗？

All the examples I find use a foreach loop. Prior to adding the other 2 classes I used a foreach loop fine, but now I got to get the indexing to work right. Any suggestions?

static void Main(string[] args)
        {
            DataTable table = new DataTable("IrisTrainingData");
            table.Columns.Add("SepalLength", typeof(double));
            table.Columns.Add("SepalWidth", typeof(double));
            table.Columns.Add("PedalLength", typeof(double));
            table.Columns.Add("PedalWidth", typeof(double));
            table.Columns.Add("Class", typeof(double));

            //training data
            table.Rows.Add(5.1, 3.5, 1.4, 0.2, 1);
            table.Rows.Add(4.9, 3.0, 1.4, 0.2, 1);
            table.Rows.Add(4.7, 3.2, 1.3, 0.2, 1);
            table.Rows.Add(4.6, 3.1, 1.5, 0.2, 1);
            table.Rows.Add(5.0, 3.6, 1.4, 0.2, 1);
            table.Rows.Add(5.4, 3.9, 1.7, 0.4, 1);
            table.Rows.Add(4.6, 3.4, 1.4, 0.3, 1);
            table.Rows.Add(5.0, 3.4, 1.5, 0.2, 1);
            table.Rows.Add(4.4, 2.9, 1.4, 0.2, 1);
            table.Rows.Add(4.9, 3.1, 1.5, 0.1, 1);
            table.Rows.Add(5.4, 3.7, 1.5, 0.2, 1);
            table.Rows.Add(4.8, 3.4, 1.6, 0.2, 1);
            table.Rows.Add(4.8, 3.0, 1.4, 0.1, 1);
            table.Rows.Add(4.3, 3.0, 1.1, 0.1, 1);
            table.Rows.Add(5.8, 4.0, 1.2, 0.2, 1);
            table.Rows.Add(5.7, 4.4, 1.5, 0.4, 1);
            table.Rows.Add(5.4, 3.9, 1.3, 0.4, 1);
            table.Rows.Add(5.1, 3.5, 1.4, 0.3, 1);
            table.Rows.Add(5.7, 3.8, 1.7, 0.3, 1);
            table.Rows.Add(5.1, 3.8, 1.5, 0.3, 1);
            table.Rows.Add(5.4, 3.4, 1.7, 0.2, 1);
            table.Rows.Add(5.1, 3.7, 1.5, 0.4, 1);
            table.Rows.Add(4.6, 3.6, 1.0, 0.2, 1);
            table.Rows.Add(5.1, 3.3, 1.7, 0.5, 1);
            table.Rows.Add(4.8, 3.4, 1.9, 0.2, 1);


            // Variables to total the values of the four columns
            double total1 = 0.0;
            double total2=0.0;
            double total3=0.0;
            double total4=0.0;
              
                      

           //Calculate the sum of training data
           for (int i = 0; i < 25; i++)
           {
               total1 += table.Rows[i]["SepalLength"]; <- I know this is wrong

               total2 += (double)row["SepalWidth"];
               total3 += (double)row["PedalLength"];
               total4 += (double)row["PedalWidth"];
           }

推荐答案

var tableFiltered = table.AsEnumerable().Where(p => p.Field<double>("Class") == 1);
double total1 = tableFiltered.Sum(p => p.Field<double>("SepalLength"));
double total2 = tableFiltered.Sum(p => p.Field<double>("SepalWidth"));
double total3 = tableFiltered.Sum(p => p.Field<double>("PedalLength"));
double total4 = tableFiltered.Sum(p => p.Field<double>("PedalWidth"));

要计算方差，均值，标准偏差，您可以将此扩展方法类添加到项目中;

To calculate variance, mean, standart deviation you can add this extension methods class to your project;

public static class MyListExtensions
    {
        public static double Mean(this List<double> values)
        {
            return values.Count == 0 ? 0 : values.Mean(0, values.Count);
        }

        public static double Mean(this List<double> values, int start, int end)
        {
            double s = 0;

            for (int i = start; i < end; i++)
            {
                s += values[i];
            }

            return s / (end - start);
        }

        public static double Variance(this List<double> values)
        {
            return values.Variance(values.Mean(), 0, values.Count);
        }

        public static double Variance(this List<double> values, double mean)
        {
            return values.Variance(mean, 0, values.Count);
        }

        public static double Variance(this List<double> values, double mean, int start, int end)
        {
            double variance = 0;

            for (int i = start; i < end; i++)
            {
                variance += Math.Pow((values[i] - mean), 2);
            }

            int n = end - start;
            if (start > 0) n -= 1;

            return variance / (n);
        }

        public static double StandardDeviation(this List<double> values)
        {
            return values.Count == 0 ? 0 : values.StandardDeviation(0, values.Count);
        }

        public static double StandardDeviation(this List<double> values, int start, int end)
        {
            double mean = values.Mean(start, end);
            double variance = values.Variance(mean, start, end);

            return Math.Sqrt(variance);
        }
    }

那么你可以简单地找到一列这样的变体;

Then you can simply find a variation of one column like that;

var tableFiltered = table.AsEnumerable().Where(p => p.Field<double>("Class") == 1);
double varSepalLen = tableFiltered.Select(p => p.Field<double>("SepalLength")).ToList().Variance();

Double nrClasses =  Convert.ToDouble(table.Compute("max(Class)", string.Empty));
double[] total1 = new double[nrClasses];
double[] total2 = new double[nrClasses];
double[] total3 = new double[nrClasses];
double[] total4 = new double[nrClasses];

用

替换你的循环

replace your loop with

foreach (DataRow row in table.Rows)
{
   double nrClass = row["Class"] == DBNull.Value ? 0 : Convert.ToDouble(row["Class"]) -1;
    total1[nrClass] += row["SepalLength"] == DBNull.Value ? 0: Convert.ToDouble(row["SepalLength"]);
    total2[nrClass] += row["SepalWidth"] == DBNull.Value ? 0: Convert.ToDouble(row["SepalWidth"]);
    total3[nrClass] += row["PedalLength"] == DBNull.Value ? 0: Convert.ToDouble(row["PedalLength"]);
    total4[nrClass] += row["PedalWidth"] == DBNull.Value ? 0: Convert.ToDouble(row["PedalWidth"]);
}

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