SSRS Get value of previous row in a matrix (cannot use previous function because it's a matrix)

Question

I have a SSRS report which uses a matrix for a crosstab effect.
Each row contains about 10 score values in 10 columns respectively. I need each row to check against the previous row, and i need each score value in each column to be compared to the corresponding column score value in the previous row. 
If the current score is greater than the corresponding previous score (in the previous row), then i want to change the background of the cell.
if the current score is smaller than the previous, then it's a different color.
if they are equal, or it's the first row in the matrix table, then leave white.
I have found custom code functions to use in the SSRS expression fields, but every single one of them compares against the previous COLUMN value and not the previous ROW value which is what i need. the "Previous" function would be perfect if i
could use it in a matrix but i can't. (i keep getting error "The use of a Previous aggregate function in a tablix cell is not supported"). looking around it turns out that matrices are arrange in groups and not in rows which is why Previous can't
be used and the only way is with custom code.
Please help. if you have any custom code samples that achieve what i need, please share, or give me advice on how to achieve this. 
Thank you

Answer 1

I figured it out. Maybe it can help someone else in the future:
Public Shared count as Integer = 0
Public Shared currentRow As Integer = 1
Public Shared MatrixStructures As New System.Collections.Generic.List(Of MatrixStructure)()
Public Shared Function GetCellColor(row as Integer, score as Integer)
If (row > currentRow) Then
count = 0
currentRow = row
End If
count = count + 1
Dim matrixStructure As New MatrixStructure()
matrixStructure.RowIndex = row
matrixStructure.ColumnIndex = count
matrixStructure.ScoreValue = score
MatrixStructures.Add(matrixStructure)
If score = 0 Then
Return "White"
End If
Dim val As MatrixStructure = MatrixStructures.Find(Function(s As MatrixStructure)
Return s.GetRowIndex() = row - 1 AndAlso s.GetColumnIndex() = count
End Function)
If (Not (val Is Nothing)) Then
If val.scoreValue = 0 Then
Return "White"
End If
If score >= val.scoreValue + 2 Then
Return "Green"
ElseIf score <= val.scoreValue - 2 Then
Return "Red"
End If
End If
Return "White"
End Function
Public Class MatrixStructure
Public rowIndex As Integer
Property GetRowIndex() As Integer
Get
Return rowIndex
End Get
Set(ByVal Value As Integer)
rowIndex = Value
End Set
End Property
Public columnIndex As Integer
Property GetColumnIndex() As Integer
Get
Return columnIndex
End Get
Set(ByVal Value As Integer)
columnIndex = Value
End Set
End Property
Public scoreValue As Integer
Property GetScoreValue () As Integer
Get
Return scoreValue
End Get
Set(ByVal Value As Integer)
scoreValue = Value
End Set
End Property
End Class
and to pass the current row number from the expression i use this
Ceiling(RowNumber(NOTHING) / 10)
i divide the row number by 10 because there are ten columns. if you don't know the number of columns, or it's a variable number, then return it from the stored procedure query in the first place. that's what I had to do