Can you Join your data, That opens up a World of easy life for you.
Here is a thought - Parameters are global - that is they are effective throughout the entire workbook - based on your string parameter you could create your first set on calculated field to use with data from your primary sources and then create a second set (same as the first) to use in your secondary source -
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@Deepak: Not sure what join you mean. My two data sources are blended.
@Jim: Thanks. Could you elaborate on "create your first set on calculated field"? Will a set help me re-use my calculated fields across data sources?