There is no easy way (except by using macros) to obtain the currently selected expression from a group. An expression group also doesn't have a label, so GetCurrentField() won't work.
However, you can build upon a workaround that was initially suggested by JohnW in How to get the used expression?. It goes as follows:
- In your script, create a date island with two fields that have the names of your expressions both as name and as content. If for example you use the example from your OP, call the fields Volume and Sales and add a singe row with Volume and Sales
- Create a cyclic dimension group that includes these two fields. Add the group as a dimension to your chart. Place the group icon somewhere on your chart.
- Pull the two expressions out of the expression group, and either combine them in a single IF() construct (one expression switches between two real expressions, depending on the currently selected field in the newly created dimension group - see below) or leave them as they are and give each a conditional show depending on which field is selected in the cyclic group you came to create.
- Define two real dimension groups: one with fields A and C and one with fields B and C.
- Add those two dimension groups to your chart, but give each one the same conditional show expression as the conditional show of the corresponding chart expression.
- Now try it out.
For getting the currently selected dimension from a cyclic group, you can use the following:
=GetCurrentField(DimensionGroupName)
which you can use to correctly label the following combined expression:
=IF (GetCurrentField(DimensionGroupName)='Sales', Sum(SalesData), Sum(VolumeData))
IF you keep two separate expressions, use conditional show expressions like:
GetCurrentField(DimensionGroupName) = 'Sales'
GetCurrentField(DimensionGroupName) = 'Volume'
Note: of course the fields in the new Cyclic group cannot have the same names as the Sales and Volume fields in your facts table.
Best,
Peter
