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How to: Reorder the Fields of a Delimited File (LINQ) (Visual Basic)

  • Artikkeli

A comma-separated value (CSV) file is a text file that is often used to store spreadsheet data or other tabular data that is represented by rows and columns. By using the Split method to separate the fields, it is very easy to query and manipulate CSV files by using LINQ. In fact, the same technique can be used to reorder the parts of any structured line of text; it is not limited to CSV files.

In the following example, assume that the three columns represent students' "last name," "first name", and "ID." The fields are in alphabetical order based on the students' last names. The query produces a new sequence in which the ID column appears first, followed by a second column that combines the student's first name and last name. The lines are reordered according to the ID field. The results are saved into a new file and the original data is not modified.

To create the data file

  1. Copy the following lines into a plain text file that is named spreadsheet1.csv. Save the file in your project folder.

    Adams,Terry,120
Fakhouri,Fadi,116
Feng,Hanying,117
Garcia,Cesar,114
Garcia,Debra,115
Garcia,Hugo,118
Mortensen,Sven,113
O'Donnell,Claire,112
Omelchenko,Svetlana,111
Tucker,Lance,119
Tucker,Michael,122
Zabokritski,Eugene,121

Example

Class CSVFiles

    Shared Sub Main()

        ' Create the IEnumerable data source.
        Dim lines As String() = System.IO.File.ReadAllLines("../../../spreadsheet1.csv")

        ' Execute the query. Put field 2 first, then
        ' reverse and combine fields 0 and 1 from the old field
        Dim lineQuery = From line In lines
                        Let x = line.Split(New Char() {","})
                        Order By x(2)
                        Select x(2) & ", " & (x(1) & " " & x(0))

        ' Execute the query and write out the new file. Note that WriteAllLines
        ' takes a string array, so ToArray is called on the query.
        System.IO.File.WriteAllLines("../../../spreadsheet2.csv", lineQuery.ToArray())

        ' Keep console window open in debug mode.
        Console.WriteLine("Spreadsheet2.csv written to disk. Press any key to exit")
        Console.ReadKey()
    End Sub
End Class
' Output to spreadsheet2.csv:
' 111, Svetlana Omelchenko
' 112, Claire O'Donnell
' 113, Sven Mortensen
' 114, Cesar Garcia
' 115, Debra Garcia
' 116, Fadi Fakhouri
' 117, Hanying Feng
' 118, Hugo Garcia
' 119, Lance Tucker
' 120, Terry Adams
' 121, Eugene Zabokritski
' 122, Michael Tucker

See also