Custom expressions
You are not limited to the pre-defined aggregation methods; you can create your own expressions and apply them to the visualization axes. The custom expressions that you create can contain mathematical as well as logical parts. The result of such an expression on an axis is immediately reflected in the visualization, just as the result of any of the pre-defined aggregation methods.

You can anytime change the expressions on the visualization axes either by using the pre-deined aggregation methods, or by creating your own custom expressions.
Because a custom expression is applied on a certain visualization axis, only the current visualization is affected, and other visualizations in the analysis stay unaffected. The results of the expression are not added to the data table, and with that, not available elsewhere in the analysis.
Whenever the visualization properties change, for example, by filtering, re-evaluations of the custom expressions take place automatically, and only those rows of data that are available after filtering are used in the calculations.
For information on how to create a custom expression, see Applying a custom expression.
Custom expressions work as predefined aggregations
Custom expressions work in the same way as predefined aggregations, with the distinction that custom expressions are not predefined by the system; they are configured by you. The similarity is illustrated in the example below that compares a well-known aggregation, average (Avg), and a custom expression that delivers the same result.


The next bar chart shows the same result. Instead of using the predefined aggregation, the following custom expression has been applied:
Sum([Value])/Count([Item])

- Applying a custom expression
You can create your own expression using various mathematical and logical functions, and apply it directly on an axis in a visualization. - Examples of custom expressions
You can create your own expressions using various mathematical and logical functions, and apply them directly on an axis in a visualization. The following examples give you an idea of how custom expressions can be used to retrieve more information about your data. - Axes in expressions
When creating custom expressions, you might need to refer to an axis from the visualization in the expression. Below is a list of the available axes for different visualization types. Some of the axes can be useful in OVER expressions, whereas others are only used when defining rules or reference lines.