(NET) NET (2018)

Processing CSV files by CsvHelper.

CSV files is a simple text file, therefore it can be read by any way, for example this LINQ query create IEnumerable interface for CSV files contains rowheader and some digit. By one string of code CSV file has been read and has been calculate average and summary for each line.



Because this task is so simple, and CSV files is so spread, there are a lot of library to read CSV LinqToCsv, Linq.Csv, CsvTools. LINQ-to-CSV-library etc, but in this page I show template to use another library CsvHelper.


This library can read CSV to typed memory (class with field definition) and to untyped dynamic memory (DataTable), this is documentation for this library https://joshclose.github.io/CsvHelper/examples.


This is my template to read CSV by this lib to DataTable.



 346:      Function ReadCSV(CsvFileName As String) As DataTable
 347:          ErrRowListNumber = New List(Of Integer)
 348:          Dim RDR = New StreamReader(CsvFileName)
 349:          Dim CSV = New CsvHelper.CsvReader(RDR)
 350:          CSV.Configuration.BadDataFound = (Sub(X) MsgBox("Import this row is impossible (incorrect delimiter):" & vbCrLf & X.RawRecord))
 351:          CSV.Configuration.Delimiter = ";"
 352:          Dim DR = New CsvHelper.CsvDataReader(CSV)
 353:          Dim DT As New DataTable()
 354:          DT.Load(DR, LoadOption.OverwriteChanges, AddressOf CsvHelperLoadError)
 355:          RDR.Close()
 356:          RDR.Dispose()
 357:          CSV = Nothing
 358:          DR.Close()
 359:          DR.Dispose()
 360:          DR = Nothing
 361:          Return DT
 362:      End Function
 363:   
 364:      Dim ErrRowListNumber As List(Of Integer)
 365:      Sub CsvHelperLoadError(sender As Object, e As FillErrorEventArgs)
 366:          e.DataTable.Rows.Add()
 367:          Dim Str1 As New Text.StringBuilder
 368:          For i As Integer = 0 To e.Values.Count - 1
 369:              Str1.AppendLine("(" & i & ")" & e.Values(i))
 370:          Next
 371:          MsgBox("Import this row is impossible (more than " & e.Values.Count & " column):" & vbCrLf & Str1.ToString)
 372:          ErrRowListNumber.Add(e.DataTable.Rows.Count)
 373:          e.Continue = True
 374:      End Sub

Because most problem in practice is malformed CSV, this reader has two callback to process malformed CSV rows - CsvHelperLoadError and expression in string 354. However, I still don't know how to processed malformed row by own code and how to add it to datatable and I'm forced to ignore malformed rows question.


But when data has been read to Datatable it can by filtered and sorted so simple. For example, this is simplest way to use Datatable - only ordered rows.


 670:          Dim DT1 As DataTable = ReadCSV(IO.Path.Combine(SelectedTempPath, WestlawSelectedListViewFileName))
 671:          Dim DV2 As DataView = DT1.DefaultView
 672:          DV2.Sort() = e.Argument & " asc"
 673:          Dim DT2 As DataTable = DV2.ToTable
 ....   

And this is fragment of my real code from another project to do filtered and ordered rows in DataTable.


 380:                  Dim DT As DataTable = ReadCSV(OutFileName)
 381:                  Dim DTF As DataTable = FilterRowAndColumn(DT, UnicourtOrderComboBox.SelectedItem)
 ....   
 427:      Function FilterRowAndColumn(DT As DataTable, SortBy As String) As DataTable
 428:          Dim ERC1 As EnumerableRowCollection(Of DataRow) = DT.AsEnumerable.Where(Function(X) X.Field(Of String)("Party Type") <> "Defendant")
 429:          Dim DT1 As DataTable = ERC1.CopyToDataTable()
 430:          Dim ERC2 As EnumerableRowCollection(Of DataRow) = DT1.AsEnumerable.Where(Function(X) X.Field(Of String)("Party Representation Type") <> "Attorney Represented")
 431:          Dim DT2 As DataTable = ERC2.CopyToDataTable()
 432:          Dim DT3 As DataTable
 433:          Dim ERC3 As EnumerableRowCollection(Of DataRow)
 434:          If AllowCompaniesCheckBox.Checked And IncludeIndividualCheckBox.Checked Then
 435:              ERC3 = DT2.AsEnumerable.Where(Function(X) X.Field(Of String)("Party Entity Type") = "Company" Or X.Field(Of String)("Party Entity Type") = "Individual")
 436:              DT3 = ERC3.CopyToDataTable()
 437:          ElseIf AllowCompaniesCheckBox.Checked And Not IncludeIndividualCheckBox.Checked Then
 438:              ERC3 = DT2.AsEnumerable.Where(Function(X) X.Field(Of String)("Party Entity Type") = "Company")
 439:              DT3 = ERC3.CopyToDataTable()
 440:          ElseIf Not AllowCompaniesCheckBox.Checked And IncludeIndividualCheckBox.Checked Then
 441:              ERC3 = DT2.AsEnumerable.Where(Function(X) X.Field(Of String)("Party Entity Type") = "Individual")
 442:              DT3 = ERC3.CopyToDataTable()
 443:          ElseIf Not AllowCompaniesCheckBox.Checked And Not IncludeIndividualCheckBox.Checked Then
 444:              DT3 = DT2
 445:          End If
 446:          'DataTable.Clone function only the schema will be copied. But DataTable.Copy() copies both the structure and data
 447:          Dim DT4 As New DataTable
 448:          DT4.Columns.Add("Party Name", GetType(String))
 449:          DT4.Columns.Add("Source", GetType(String))
 450:          DT4.Columns.Add("Street Address", GetType(String))
 451:          DT4.Columns.Add("City", GetType(String))
 452:          DT4.Columns.Add("State", GetType(String))
 453:          DT4.Columns.Add("Zip", GetType(String))
 454:          DT4.Columns.Add("URL", GetType(String))
 455:          DT4.Columns.Add("ID", GetType(String))
 456:          DT4.Columns.Add("Name", GetType(String))
 457:          DT4.Columns.Add("Number", GetType(String))
 ....   
 521:          For K As Integer = 0 To DT3.Rows.Count - 1
 522:              DT4.Rows.Add()
 523:              For I As Integer = 0 To DT4.Columns.Count - 1
 524:                  For J As Integer = 0 To DT3.Columns.Count - 1
 525:                      If DT4.Columns(I).ColumnName = DT3.Columns(J).ColumnName.Replace("Case ", "") Then
 526:                          DT4(DT4.Rows.Count - 1)(I) = DT3(K)(J)
 527:                          GoTo NextRow
 528:                      End If
 529:                  Next
 530:  NextRow:
 531:              Next
 532:          Next
 533:          Dim DV4 As DataView = DT4.DefaultView
 534:          DV4.Sort() = SortBy & " asc"
 535:          Dim DT5 As DataTable = DV4.ToTable
 536:          Return DT5
 537:      End Function



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