Inner and Outer Set Expressions

[Jennell_McIntire]

Today I am going to blog about inner and outer set expressions. If you have ever used set analysis in your measure expressions, then you will like this new capability. Set analysis is a very powerful feature often used to define a scope that may differ from the scope that is defined by making selections in an app. For example, in the set expression below the sales are summed where the product line is camping equipment. This is considered an inner set expression and probably familiar to those who use set analysis. The set expression is in the aggregate function which is sum in this case.

If this expression was written as an outer set expression, the set expression would be outside of the aggregate function as seen below. When using an outer set expression, it must be before the scope. In this example, both the inner and outer expressions return the same result.

Now, where the outer set expression is helpful is when you have more than one aggregate function in your expression. For example, in the inner set expression below, there are three sum aggregate functions and in each one, set analysis is being used to set the scope to camping equipment.

Using an outer set expression, this expression can be written like this:

Notice that the set expression sits outside of the expression and at the beginning of the scope. Written this way, [Product Line]={'Camping Equipment'} is applied to all the aggregate functions. This is a cleaner way to write the expression and ensures that it is applied to all the aggregate functions. The outer set expression can also be used with a master measure. Assume I have master measures named Sales and Margin %. I can use outer set expressions like the ones below.

A set expression, like the outer set expressions above, are applied to the entire expression. If the set expressions were in brackets, then the set expression applies only to the aggregate functions within the brackets. For example, the set expression below is in parentheses which means that it only applies to the aggregate functions within the parentheses and not to the aggregate function that sits outside of the parentheses. Written this way, the resulting value will differ from the set expression without any brackets/parentheses.

A few things to remember about set expressions. Inner set expressions have precedence over outer set expressions and if the inner set expression has a set identifier, it replaces the context. Otherwise, the inner set expression is merged with the outer set expression. Check out Qlik Help for more examples and rules around inner and outer set expressions and try it for yourself in your next app.

Thanks,

Jennell