逐列获取不同的值

Question

Have to get each columns distinct data and store to the Dictionary (or array) using Excel.interop. I have tried the following code, but it does not align with Excel.interop.

      var excel = new ExcelQueryFactory("worksheetFileName");
      var distinctNames = (from row in excel.WorkSheet() select row["ColB"]).Distinct();

Please provide the Excel.Interop snippet/code to get distinct values column by column and store in array.

Answer 1

For this operation it does not make sense to using Excel automation, instead the prudent course of action is to work with OleDb unless there is a sound reason for using Excel automation.

Example, figure 1 is a function to create a connection string which can be used in any project while figure 2 is for reading data.

To work with Excel automation we open ourselves up to objects not being disposed of if there is a crash or that you do not code properly (this I call the two dot rule) when objects can't be released because of how you created and used automation objects which does not happen with OleDb. Now if you wanted formatting than we move to automation.

public string ConnectionString(string FileName, string Header)
{
    OleDbConnectionStringBuilder Builder = new OleDbConnectionStringBuilder();
    if (System.IO.Path.GetExtension(FileName).ToUpper() == ".XLS")
    {
        Builder.Provider = "Microsoft.Jet.OLEDB.4.0";
        Builder.Add("Extended Properties", string.Format("Excel 8.0;IMEX=1;HDR={0};", Header));
    }
    else
    {
        Builder.Provider = "Microsoft.ACE.OLEDB.12.0";
        Builder.Add("Extended Properties", string.Format("Excel 12.0;IMEX=1;HDR={0};", Header));
    }

    Builder.DataSource = FileName;

    return Builder.ConnectionString;
}

Code to read the first column in Sheet2 and get distinct values, in this case I am working against a column with dates as string into List where the file resides in the same folder as the app executable

private List<string> DemoDistinct()
{
    List<string> dateList = new List<string>();
    DataTable dt = new DataTable();

    using (OleDbConnection cn = new OleDbConnection { ConnectionString = ConnectionString(System.IO.Path.Combine(Application.StartupPath, "WS1.xlsx"), "Yes") })
    {
        cn.Open();

        using (OleDbCommand cmd = new OleDbCommand
        {
            CommandText = "SELECT DISTINCT [Dates] FROM [Sheet2$]",
            Connection = cn
        }
         )
        {
            OleDbDataReader dr = cmd.ExecuteReader();
            dt.Load(dr);
            dateList = dt
                .AsEnumerable()
                .Select(row => row.Field<DateTime>("Dates").ToShortDateString()).ToList();                      
        }
    }

    return dateList;
}