VB.Net editing a CSV (or delimited file) - vb.net

Question

I would like to know a way (of course I want to know the best way) to edit a csv file, preferably without having to read the original and write the results to a new one.
Example 1: I want to split the contents of a column into two columns 123abc into 123, abc
Example 2: I want to remove letters from the beginning of a column AB123 into 123
Clarification: I do not need help solving my examples; I just need to be pointed in the right direction of reading and editing the same file.
Here is a code example of using a temporary file that seems to me is too slow
Dim currentLine as string()
tempFile.AutoFlush = True
Do Until origFile.EndOfData
currentLine = origFile.ReadFields
currentLine(1) = currentLine(1).Replace("ABC","") 'would convert ABC123 to 123
For index as Integer = 0 to currentLine.Count - 2
tempFile.Write(currentLine(index) & ",")
Next
tempFile.Write(currentLine(currentLine.Count - 1))
tempFile.WriteLine()
Loop
tempFile.Flush()
tempFile.Dispose()
origFile.Dispose()
IO.File.Copy(tempFile,OrigFile,True)
IO.File.Delete(tempFile)

Answer 1

You really will be best off writing a new file. You can write to a temporary file, delete the old file and rename the new file as the old file.
Something like:
Imports System.IO
Module Module1
Sub Main()
Dim tempfile = Path.GetTempFileName()
Dim inputFile = "C:\Temp\input.txt"
Using sw = New StreamWriter(tempfile)
Using MyReader As New Microsoft.VisualBasic.FileIO.TextFieldParser(inputFile)
MyReader.TextFieldType = Microsoft.VisualBasic.FileIO.FieldType.Delimited
MyReader.Delimiters = New String() {","}
Dim currentRow As String()
While Not MyReader.EndOfData
Try
currentRow = MyReader.ReadFields()
If currentRow.Count >= 2 Then
currentRow(1) = currentRow(1).Replace("ABC", "")
End If
sw.WriteLine(String.Join(",", currentRow))
Catch ex As Microsoft.VisualBasic.FileIO.MalformedLineException
MsgBox("Line " & ex.Message & " is invalid. Skipping")
End Try
End While
End Using
End Using
File.Delete(inputFile)
File.Move(tempfile, inputFile)
End Sub
End Module
(Basically copying the TextFieldParser example from http://msdn.microsoft.com/en-us/library/microsoft.visualbasic.fileio.textfieldparser.readfields.aspx )

Answer 2

You can use ADO to connect to the CSV file. See here for more info:
How to read a CSV file into a .NET Datatable
However, I would recommend simply loading it into an array and then writing it back out with simple file IO methods. It's just a lot less code and overhead:
For Each row As String In File.ReadAllLines("C:\test.csv")
For Each column As String In row.Split(New String() {","}, StringSplitOptions.None)
' Do work
Next
Next
And then something like this to save the file:
File.WriteAllLines(rows)