How to Extract Data from a Datatable

How do I extract data from a DataTable?

The DataTable has a collection .Rows of DataRow elements.

Each DataRow corresponds to one row in your database, and contains a collection of columns.

In order to access a single value, do something like this:

 foreach(DataRow row in YourDataTable.Rows)
 { 
     string name = row["name"].ToString();
     string description = row["description"].ToString();
     string icoFileName = row["iconFile"].ToString();
     string installScript = row["installScript"].ToString();
 }

How To Extract Values From DataTable To List in C#

To extract data from a data table use the .Field<T>() extension method from System.Data.DataSetExtensions. Please see the documentation DataRow.Field.

You need to create a list of type PurchaseInvoice and iterate over the DataRow collection table.Rows.

Please see example below:

// create a list for your invoices
List<PurchaseInvoice> invoices = new List<PurchaseInvoice>();

foreach (DataRow row in dtPurchaseInvoice.Rows)
{   //                                   ^ Rows
    // create invoice
    PurchaseInvoice invoice = new PurchaseInvoice();

    // get an int
    invoice.PurchaseInvoiceNo = row.Field<int>("PurchaseInvoiceNo"); 

    // get a string
    invoice.CustomerName = row.Field<string>("CustomerName");

    // get a DateTime
    invoice.PurchaseDate = row.Field<DateTime>("PurchaseDate");

    // get a double
    invoice.PurchaseValue = row.Field<double>("PurchaseValue");

    // add invoice to list     
    invoices.Add(invoice);
}

Using .Field<T>() extension means you do not need to convert/cast the object into the correct type - it is handled by the extension for you.

It also works with nullable fields:

DateTime? date = row.Field<DateTime?>("PurchaseDate");

Extract data from datatable

In order to get the sheet name, using oledb, you will need to use code that looks something like this (thanks to this SO post and answer):

DataTable dtSheets = con.GetOleDbSchemaTable(OleDbSchemaGuid.Tables, null);
     List<string> sheets= new List<string>();
     foreach (DataRow dr in dtSheets.Rows)
     {
        if (dr["TABLE_NAME"].ToString().Contains("$"))//checks whether row contains '_xlnm#_FilterDatabase' or sheet name(i.e. sheet name always ends with $ sign)
        {
             sheets.Add(dr["TABLE_NAME"].ToString());
        } 
     }

Below is how you access the values from a datatable:

var someValue = dt.Rows[i][j]

You need to get the item at the column index (j) of the row, at the row index (i), of the current datatable (dt).

Conversely, you can use the name of the column as well.

var someValue = dt.Rows[i]["columnName"]

Extracting data from datatable with conditions c#

You can do the following:

private void GetRowsByFilter()
{
    DataTable yourDataTable = new DataTable(); //Your DataTable is supposed to have the data
    // Presuming the DataTable has a column named user.
    string expression;
    expression = "user = \"msalmon\"";
    DataRow[] foundRows;

    // Use the Select method to find all rows matching the filter.
    foundRows = table.Select(expression);

    // Print column 0 of each returned row.
    for(int i = 0; i < foundRows.Length; i ++)
    {
        Console.WriteLine(foundRows[i][0]);
    }
}

Extract only filtered data from table in Dash Python

Globals are generally something to avoid, especially in Dash. The good news is, the fix should be pretty easy here. Since you're using custom filtering on the back end, rather than native, front-end filtering, I think what you need is to add the data prop to your download callback as state. If you'd been using front-end filtering, you'd have to use the derived_virtual_data prop instead. The following should work.

@app.callback(
    Output("download-dataframe-csv", "data"),
    Input("button_export", "n_clicks"),
    State("table-sorting-filtering", "data"),
    prevent_initial_call=True,
)
def export_on_click(n_clicks, table_data):
    df = pd.DataFrame.from_dict(table_data)
    return dcc.send_data_frame(df.to_excel, "export.xlsx")

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