How to Concatenate an Excel File Using a DataTable?

Question

I have a DataTable being generated using the C# NI DAQmx code. I want to take this DataTable and put it in an excel file when a CheckBox is checked. The DAQmx code records this data 'x' number of samples at a time. When this number is high, the program is slow, but it still works. I want to record a low number of samples at a time, and then save that data into an excel file.

In my current code, the data in the excel file is constantly overwritten. This is not desirable, as I need all recorded data.

Currently the data will actively record when the box is checked, but it will not concatenate. I have tried many searches and explored many methods for this, but I haven't quite been able to adapt anything for my needs.

Relevant code will be included below. Any help is appreciated, thanks.

Note: Data does not have to be a .xlsx file. It can be a .csv

This code is the DataTable generation via DAQmx:

    private void DataToDataTable(AnalogWaveform<double>[] sourceArray, ref DataTable dataTable)
    {
        // Iterate over channels
        int currentLineIndex = 0;
        string test = currentLineIndex.ToString();

        foreach (AnalogWaveform<double> waveform in sourceArray)
        {
            for (int sample = 0; sample < waveform.Samples.Count; ++sample)
            {
                if (sample == 50)
                    break;

                dataTable.Rows[sample][currentLineIndex] = waveform.Samples[sample].Value;
            }
            currentLineIndex++;       
        }
    }

    public void InitializeDataTable(AIChannelCollection channelCollection, ref DataTable data)
    {
        int numOfChannels = channelCollection.Count;
        data.Rows.Clear();
        data.Columns.Clear();
        dataColumn = new DataColumn[numOfChannels];
        int numOfRows = 50;

        for (int currentChannelIndex = 0; currentChannelIndex < numOfChannels; currentChannelIndex++)
        {
            dataColumn[currentChannelIndex] = new DataColumn()
            {
                DataType = typeof(double),
                ColumnName = channelCollection[currentChannelIndex].PhysicalName
            };
        }

        data.Columns.AddRange(dataColumn);

        for (int currentDataIndex = 0; currentDataIndex < numOfRows ; currentDataIndex++) 
        {
            object[] rowArr = new object[numOfChannels];
            data.Rows.Add(rowArr);
        }
    }

This is my current method of saving to an Excel file:

        private void Excel_cap_CheckedChanged(object sender, EventArgs e)
    {

                   int i = 0;
        for (excel_cap.Checked = true; excel_cap.Checked == true; i ++) {

            {
                StringBuilder sb = new StringBuilder();

                IEnumerable<string> columnNames = dataTable.Columns.Cast<DataColumn>().
                                                  Select(column => column.ColumnName);
                sb.AppendLine(string.Join(",", columnNames));

                foreach (DataRow row in dataTable.Rows)
                {
                    IEnumerable<string> fields = row.ItemArray.Select(field => field.ToString());
                    sb.AppendLine(string.Join(",", fields));
                }

                File.AppendAllText(filename_box.Text, sb.ToString());

            }
        }
    }

Answer 1

Since you mentioned it does not have to be Excel, it could be a CSV, then you can use your CSV code but change the File.WriteAllText line to File.AppendAllText which will append the text rather than replacing the existing file. AppendAllText will create the file if it doesn't exist.

File.AppendAllText("test.csv", sb.ToString());