> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cfo.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# How aggregation works

Aggregation combines several values into one result. In formulas, aggregation can happen in three related ways.

## 1. Property aggregation

A property has a default way to roll underlying values into a model cell. Metrics normally use `sum`. Dimensions normally use `first` because they describe a group rather than a numeric total.

This behavior applies when source data contains several records for the same model position.

## 2. Multi-value references

A formula reference can deliberately select several values. For example:

```text theme={null}
Revenue[Department: ANY]
```

This selects Revenue across all Department values. If no aggregation function is written, a multi-value metric lookup uses `sum`.

It is clearer to write the intended aggregation when the choice matters:

```text theme={null}
average(Revenue[Department: ANY])
```

## 3. Aggregation functions

Aggregation functions let you choose how several values become one result. Supported functions include:

* `sum`
* `average`
* `min` and `max`
* `count`
* `median`
* `stdev` and `var`
* `first` and `last`

## Example

If Department Revenue is Sales 50, Marketing 30, and Engineering 20:

* `sum(Revenue[Department: ANY])` returns 100
* `average(Revenue[Department: ANY])` returns about 33.33
* `max(Revenue[Department: ANY])` returns 50
* `count(Revenue[Department: ANY])` returns 3 when all three values are present

## Write the business meaning

Use the aggregation that matches the question. Totals usually use `sum`. Rates and ratios often need to be calculated from their underlying totals rather than averaged after the fact.