将数据表与条件合并

Question

I would like to merge DataTable s in a list using sum or average depending on conditions. For example:

private DataTable getData(List<DataTable> datas, string[] KeyColumnNames, string valueCol)
{
    List<DataTable> dataTables = datas;
    //if datas has 3 dataTables in it : dt1, dt2, dt3
    // then I want to create another dataTable dtAll which will have the sum of 
    // valueCol of all three datatables for the row which  will be conditioned using 
    // KeyColumnNames (can be multiple Primary keys)
    return dataTable;
}

Consider all datatables to be exactly same but different values as they are tables from similar schemas but different data centers. Thanks.

Answer 1

I would do

List<DataTable> dataTableList = dtList;
DataTable unionDataTable = new DataTable();
for(int i = 0; i < dtList.Count; i++)
    unionDataTable = Union(unionDataTable, dtList[i], "UnionDataTable");

where the Union method is defined by something like the following

public static DataTable Union(DataTable First, DataTable Second, string strReturnedTableName)
{
    // Result table.
    DataTable table = new DataTable(strReturnedTableName);

    // Build new columns.
    DataColumn[] newcolumns = new DataColumn[First.Columns.Count];
    for (int i = 0; i < First.Columns.Count; i++)
        newcolumns[i] = new DataColumn(First.Columns[i].ColumnName, First.Columns[i].DataType);

    // Add new columns to result table.
    table.Columns.AddRange(newcolumns);
    table.BeginLoadData();

    // Load data from first table.
    foreach (DataRow row in First.Rows)
        table.LoadDataRow(row.ItemArray, true);

    // Load data from second table.
    foreach (DataRow row in Second.Rows)
        table.LoadDataRow(row.ItemArray, true);

    table.EndLoadData();
    return table;
}

I hope this helps.

Edit. You can pass an Action in to the method and use this in the foreach blocks to do what you want.

Answer 2

Your question is way too vague to provide any actual code but you want to do a LINQ Join . It works about the same as a SQL join. This question shows joins in both query and method syntax How to do a join in linq to sql with method syntax? also you can look at the msdn docs here; http://msdn.microsoft.com/en-us/library/bb311040.aspx