What I want is that if you make some selections in one of the list boxes, and then make some more in others, all of them should reflect in the chart like an 'or' condition, instead of how they become 'and' selections in qlikview by default. So, I wish to see something like if my Customer is somebody, or if the product is something then give me all of them. I hope it is clear now.
I presume (since, I can't download Barry's sample app right now) that there is some gap between your approach and what Barry has suggested in his post. I would request you to download his sample app and go through it thoroughly before you attempt to implement in your app. It is imperative to understand what $Field is and how the concat() storing the selected values from fields in variables.