In some cases it might be required to parse the hierarchical data. This is a tree-structured data which has a collection of nodes while each node may contain the collection of children, and each child can have a collection of its own children and so on. Example of hierarchical data is an XML file which contains the nodes which might have sub-nodes.
This data can be parsed using loops, however this task would be complicated and code readability will be compromised. Much easier solution would be an employment of recursion technique.
This function will parse the single node (or node on a single level) and then call itself recursively to process all children nodes.
For example the following Bill Of Materials (BOM) structure represents a product.
This structure is described with the following class in the Visual Basic, where Children variable may contain children of the sub-assembly node.
Public Name As String Public Qty As Integer Public Children As Variant
In order to output the structure the following function can be written
Sub PrintBom(bom As BomItem, Optional level As Integer = 0) Dim offset As String offset = String(level, "-") Debug.Print offset & bom.Name & " (" & bom.Qty & ")" If Not IsEmpty(bom.Children) Then Dim i As Integer For i = 0 To UBound(bom.Children) Dim child As BomItem Set child = bom.Children(i) PrintBom child, level + 1 Next End If End Sub
As the result the following information will be output to the Immediate Window of VBA Editor.
A (1) -B (2) --D (1) --E (5) --F (1) -C (3)