Parent child relationships(working out parent item) for each item

[grphillips]

I have added the attachment to make it easier to understand the standard output i am trying to achieve in column C using the data in column A and column B.

What i am trying to achieve is identify the parent item automatically in column C via an excel formula or vba excel 2010 script. Surely an excel formula can do but I failed to make it work if formula in excel. i need to do this for multiple levels.

Imagine a scenario where you have list of parts to make/manufacture a car or something and you want to understand the parent item assembly for each item. The parent child relationships are worked out by the levels in column A.

I have manually populated the correct parent value in column c so you can see the standard pattern to work out the parent item. However need a forumula to do this automatically so column C values are populated automatically.

Many thanks