Use variable in equation string

[NancyG]

I have a whisker plot a specific parameter of my data, ACTUAL_CE_PH1_MJ.  One of the Expressions for the Plot is:

Fractile(Aggr(avg(ACTUAL_CE_PH1_MJ),[PROGRAM],[ACTUAL_CE_PH1_MJ]), 0.25)

I have a list box that contains a list of parameters available in the data set and I have created a variable, vPick = GetFieldSelections(listbox_name).

How do I change the formula above to use vPick instead of a specific parameter name?  I don’t understand the $ operator well enough to know why/when to use it.

I’ve tried this and while the Expression is okay (per the edit box), I don’t get the same plot as when I use hard coded the parameter name.

Fractile(Aggr(avg($(=vPick),[PROGRAM],$(=vPick)), 0.25)

Thanks for your help.

[NancyG · Accepted solution]

I figured it out..

Fractile(Aggr(avg($(vPick)),[PROGRAM],$(vPick)), 0.5)