Calculations based on Filtering

Hi,

I have a table of data from which I am trying to create a dynamic report where a weighted average growth rate can be calculated that depends on the filtering.

I have attached an example in which you’ll notice that the weighted average growth rate of all of the products is -0.90%. What I would like to be able to do is, for example, to filter on the “Long-Term” items in the “Category” column and have the weighted average growth rate calculated just for those items. Clearly the weights will change as a different set of “Values” are involved in the calculation.

Can someone please suggest the best way to go about achieving this.

Thanks!