1

拜托，如果可能的话，我想在 C# 中优化这段代码。

当少于 1000 行时，没问题。但是当我们至少有 10000 个时，它开始需要一些时间......这里有一个小基准：

  • 5000 行 => ~2s
  • 15000 行 => ~20s
  • 25000 行 => ~50s

确实，我正在寻找重复的行。

方法 SequenceEqual 检查值可能是一个问题（在我的“基准”中，我有 4 个字段被视为“keyField”......）。

这是代码：

private List<DataRow> GetDuplicateKeys(DataTable table, List<string> keyFields)
{
    Dictionary<List<object>, int> keys = new Dictionary<List<object>, int>(); // List of key values + their index in table
    List<List<object>> duplicatedKeys = new List<List<object>>(); // List of duplicated keys values 

    List<DataRow> duplicatedRows = new List<DataRow>(); // Rows that are duplicated

    foreach (DataRow row in table.Rows)
    {
        // Find keys fields values for the row
        List<object> rowKeys = new List<object>();
        keyFields.ForEach(keyField => rowKeys.Add(row[keyField]));

        // Check if those keys are already defined
        bool alreadyDefined = false;

        foreach (List<object> keyValue in keys.Keys)
        {
            if (rowKeys.SequenceEqual(keyValue))
            {
                alreadyDefined = true;
                break;
            }
        }

        if (alreadyDefined)
        {
            duplicatedRows.Add(row);

            // If first duplicate for this key, add the first occurence of this key
            if (!duplicatedKeys.Contains(rowKeys))
            {
                duplicatedKeys.Add(rowKeys);

                int i = keys[keys.Keys.First(key => key.SequenceEqual(rowKeys))];
                duplicatedRows.Add(table.Rows[i]);
            }
        }
        else
        {
            keys.Add(rowKeys, table.Rows.IndexOf(row));
        }
    }

    return duplicatedRows;
}

有任何想法吗 ？

4

2 回答 2

1

我认为这是查找重复行的最快和最短的方法：

对于 100.000 行，它在大约 250 毫秒内执行。

Main和测试数据：

static void Main(string[] args)
{
    var dt = new DataTable();
    dt.Columns.Add("Id");
    dt.Columns.Add("Value1");
    dt.Columns.Add("Value2");

    var rnd = new Random(DateTime.Now.Millisecond);
    for (int i = 0; i < 100000; i++)
    {
        var dr = dt.NewRow();
        dr[0] = rnd.Next(1, 1000);
        dr[1] = rnd.Next(1, 1000);
        dr[2] = rnd.Next(1, 1000);
        dt.Rows.Add(dr);
    }

    Stopwatch sw = new Stopwatch();
    sw.Start();
    var duplicates = GetDuplicateRows(dt, "Id", "Value1", "Value2");
    sw.Stop();
    Console.WriteLine(
        "Found {0} duplicates in {1} miliseconds.", 
        duplicates.Count,
        sw.ElapsedMilliseconds);        
    Console.ReadKey();
}

GetDuplicateRows与LINQ：

private static List<DataRow> GetDuplicateRows(DataTable table, params string[] keys)
{
    var duplicates =
        table
        .AsEnumerable()
        .GroupBy(dr => String.Join("-", keys.Select(k => dr[k])), (groupKey, groupRows) => new { Key = groupKey, Rows = groupRows })
        .Where(g => g.Rows.Count() > 1)
        .SelectMany(g => g.Rows)
        .ToList();

    return duplicates;
}

说明（对于不熟悉的人LINQ）：

最棘手的部分是GroupBy我猜。在这里，我将 a 作为第一个参数DataRow，对于每一行，我从我加入的指定键的值创建一个组键，以创建类似1-1-2. 然后第二个参数只是将组键和组行选择为一个新的匿名对象。然后我检查是否有超过 1 行并将这些组展平回列表中SelectMany。

于 2014-12-23T12:27:23.750 回答
0

Try this. Use more linq, that improve perfomance, also try with PLinq if posible.

Regards

private List<DataRow> GetDuplicateKeys(DataTable table, List<string> keyFields)
{
    Dictionary<List<object>, int> keys = new Dictionary<List<object>, int>(); // List of key values + their index in table
    List<List<object>> duplicatedKeys = new List<List<object>>(); // List of duplicated keys values 

    List<DataRow> duplicatedRows = new List<DataRow>(); // Rows that are duplicated

    foreach (DataRow row in table.Rows)
    {
        // Find keys fields values for the row
        List<object> rowKeys = new List<object>();
        keyFields.ForEach(keyField => rowKeys.Add(row[keyField]));

        // Check if those keys are already defined
        bool alreadyDefined = false;

        foreach (List<object> keyValue in keys.Keys)
        {
            if (rowKeys.Any(keyValue))
            {
                alreadyDefined = true;
                break;
            }
        }

        if (alreadyDefined)
        {
            duplicatedRows.Add(row);

            // If first duplicate for this key, add the first occurence of this key
            if (!duplicatedKeys.Contains(rowKeys))
            {
                duplicatedKeys.Add(rowKeys);

                int i = keys[keys.Keys.First(key => key.SequenceEqual(rowKeys))];
                duplicatedRows.Add(table.Rows[i]);
            }
        }
        else
        {
            keys.Add(rowKeys, table.Rows.IndexOf(row));
        }
    }

    return duplicatedRows;
}
于 2014-12-23T10:35:01.107 回答