Dim sread As New FileStream(filename, FileMode.Open, FileAccess.Read, FileShare.Read)

FileStream

Function SummarizeData(filename As String, delimiter As Char) As Dictionary(Of Integer, Integer())
    Dim limit As Integer = 0
    SummarizeData = New Dictionary(Of Integer, Integer())
    Using sr As New IO.StreamReader(filename)
        'Since we don't need the first line for the summary we can read it get _
        'the upper bound for the array, and discard the line.
        If Not sr.EndOfStream Then
            limit = sr.ReadLine.Split(delimiter).Length - 1
        Else : Throw New Exception("Empty File")
        End If
        Do Until sr.EndOfStream
            'This creates an array of integers representing the data in one line.
            Dim line = sr.ReadLine.Split(" "c).Select(Function(x) Integer.Parse(x)).ToArray
            'If the key is already in the dictionary we increment the values
            If SummarizeData.ContainsKey(line(0)) Then
                For I = 1 To limit
                    SummarizeData.Item(line(0))(I) += line(I)
                Next
            Else
            'If not we create a new element using the line as the initial values
                SummarizeData.Add(line(0), New Integer(limit) {})
                SummarizeData.Item(line(0)) = line
            End If
        Loop
    End Using
End Function

Dim results = SummarizeData("data.txt", ","c)
'If you don't need the results sorted you can gain a few fractions of a second by _
'removing the Order By clause
IO.File.WriteAllLines("results.txt", (From kvp In results
                                        Order By kvp.Key
                                        Select String.Join(",", kvp.Value)).ToArray)