Importing Huge Data Files

Excel has a limit on the number of rows you can have in a worksheet—up to 65,535 rows prior to Excel 2007. It is very possible, however, to have a raw data file that has more than this number of rows. If you need to import that file into Excel, then doing so can appear almost impossible without upgrading to Excel 2007. Even in Excel 2007 you may run into the limits of your system if you try to import a file that has hundreds of thousands of rows. There are a couple of things you can do, however.

One possibility is to make copies of the raw text file (the one you want to import) and then cut the size of each file down. For instance, if you have a total of 110,000 rows you need to import into Excel, and you are operating under the 65,535-row limit, you could make two copies of the raw text file. Delete the second half of the first text file and the first half of the second. Thus, you can import the first file (now 55,000 rows) into one worksheet and the second file (also 55,000 rows) into the second.

If you don't want to break up your input files, you might consider importing the file into Access. Unlike Excel, Access has virtually no limit on the number of rows you can import. You could then either work with the file in Access, or export portions of the file to use in Excel.

Finally, you could use a macro to import the records in the large source file. There are many ways you can do this, but the basic idea behind any approach is to fetch each row from the source file and place it in a new row of a worksheet. The macro must keep track of how many rows it's placed, and switch to a new worksheet, if necessary.

Public Sub LoadFile()
    Dim strLine As String
    Dim I As Long
    Dim J As Long
    Dim iLen As Integer
    Dim iSh As Integer
    Dim lL As Long
    Dim sDelim As String
    Dim MaxSize As Long

    sDelim = Chr(9)
    MaxSize = 65000
    I = 0
    Open "C:\MyDir\MyFile.txt" For Input As #5
    Do While Not EOF(5)
        iSh = (I / MaxSize) + 1
        lL = I Mod MaxSize
        Line Input #5, strLine
        If Right(strLine, 1) <> sDelim Then
           strLine = Trim(strLine) & sDelim
        End If
        J = 0
        Do While Len(strLine) > 1
            iLen = InStr(strLine, sDelim)
            Worksheets("Sheet" & iSh).Offset(lL, J).Value = _
              Trim(Left(strLine, iLen - 1))
            strLine = Trim(Right(strLine, Len(strLine) - iLen))
            J = J + 1
        Loop
        I = I + 1
    Loop	
    Close #5
End Sub

The macro assumes you have enough worksheets already in your workbook to contain the data, and that they are numbered Sheet1, Sheet2, Sheet3, etc. Two variables you'll want to check in the program are the settings of sDelim and MaxSize. The first specifies what character is used as a field delimiter in the information that is being read. The second specifies the maximum number of rows you want on each worksheet. (Don't set MaxSize greater than whatever your version of Excel will allow.)

Finally, note that the macro opens the text file MyFile.txt. You'll want to change this Open statement so that it opens the real source file you want to import.