PREVIOUS

In Rollforward & time series

The previous function is almost never necessary and has considerable performance and usability disadvantages over the ROLLFORWARD function. Its usage is not advised, unless you absolutely must - contact the Valsight support for information on your specific problem to evaluate if it can be modelled with a ROLLFORWARD instead.

The PREVIOUS function returns the previous period value of a node, except for the base period where it returns the value of the base node. All effects applied between the node and the base node therefore cumulate over the year. The function can be used to create models where the value of a node depends on the result for the previous period of a node higher in the value driver tree, thereby creating a loop that is resolved along the time dimension. An example is provided below, where the 'Base Cost' node depends on the final 'Cost' of the previous year, calculating the costs based on the costs of the previous year with the two drivers inflation and productivity.

Use this function when you need loop-style logic with a defined base case rather than a simple previous-period comparison.

Parameters

NodeNode referenceRequired

Input node of which the previous period value is taken, for example 'Cost'.

LevelLevel nameRequired

The time level that defines the previous value, for example "Year" where the previous of "2026" is "2025".

BaseNodeNode referenceRequired

Input node that is used to get the value of the node for the base period, for example 'Initial Cost'.

BaseValueLevel valueRequired

The value describing the base period, for example "2025".

Watch out

Example

Loop logic with an explicit base period

This example shows how PREVIOUS creates a loop along the time dimension by taking the prior year’s result and using a fixed base period to start the calculation.

Input node: 'Initial Cost'

Input node: 'Productivity Change'

Input node: 'Cost Inflation'

Formula: PREVIOUS('Cost', "Year", 'Initial Cost', "2025")

Formula: 'Base Cost' * (EXPAND(1, "Year") + 'Cost Inflation' + 'Productivity Change')

See also

ROLLFORWARD

When the same logic should be modelled in a more modern and performant way instead of relying on PREVIOUS loop logic.

PY

When you only need a simple previous-year reference instead of loop-style logic with an explicit base case.