> For the complete documentation index, see [llms.txt](https://docs.cascade.io/cascade/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.cascade.io/cascade/functions-and-expressions/functions/aggregate/countby.md).

# COUNTBY

COUNTBY( `column`, `partition column`) 

Counts the number of values within a `column` when grouped by unique values within a `partition column`.

{% hint style="info" %}
COUNTBY() is a [**window function**](/cascade/functions-and-expressions/building-expressions/guide-to-window-functions.md)**,** which performs COUNT() except partitioned by the unique values of a separate column.
{% endhint %}

### Arguments

| Input              | Description                      |
| ------------------ | -------------------------------- |
| `column`           | Column to count                  |
| `partition column` | Column containing unique values. |

### Output

Outputs a count of values when grouped by `partition column`.

### Example

In this example, we want to count the number of non-null cells in `{Adult Population}`, partitioned by `{Region}`. 

{% embed url="<https://datawrapper.dwcdn.net/ZNaf2/1/>" %}