Lookups

How to create a lookup reference

Overview

Sometimes you will need to lookup a Variable's value based on another Variable's value.

For instance, let's say we have a Model with four cost categories. For each cost category we want to apply one of two inflation types, RPI or CPI (Retail and Consumer Price Index respectively). We want to be able to dynamically choose between the two options, and for the cost item to use the correct inflation value automatically.

This is achieved using a Lookup reference - we explain how you can achieve this below.

This is the kind of operation you typically perform in Excel with an INDEX-MATCH formula, or an XLOOKUP

Lookup reference example

Example of a Lookup reference

This above example illustrates the scenario described in the Overview. Recurring cost inflation pulls its values from Inflation by type according to the selected value in Recurring cost inflation types.

Creating the Lookup reference

To create a Lookup reference, perform the following steps, as illustrated in the screenshots below:

1. In the Calculation step, add a Variable reference to the target Variable (1) (in the above example Inflation by type) using any method - by default, the reference will be a Summary of the target Variable, because the target has different Dimensions, so an Auto reference is not possible.
2. Edit the Variable Reference Calculation Part that has been added (2)

3. In the Reference type page of the dialog, select a LOOKUP reference (3)

4. This will display a new step, in which you can select a Variable with which to perform the LOOKUP (4). This Variable will need to have the same Dimensions as the Variable in which you are performing the Calculation. By default, this list will be filtered to Variables with the correct Dimensions.

Create the Lookup Variable by using the Validation data type - in this case using Inflation type as the Validation Dimension.

Creating a Lookup reference