> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify-poc.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# interpolate()

> Adjust a heartbeat aggregate with predecessor information

<Icon icon="tag" iconType="duotone" /> Since [1.15.0][toolkit-1.15.0]

Update a heartbeat aggregate to include any live ranges that should have been carried over from the last heartbeat in
the predecessor, even if there aren't heartbeats for that range in the interval covered by this aggregate. Return the
updated aggregate, which can then be used with any of the heartbeat aggregate accessors.

## Samples

Given a table called `liveness` containing weekly heartbeat aggregates in column `health` with timestamp column `date`,
use the following to get the intervals where the system was unhealthy during the week of Jan 9, 2022. This correctly
excludes any ranges covered by a heartbeat at the end of the Jan 2 week.

```sql theme={"dark"}
SELECT dead_ranges(
  interpolate(
    health,
    LAG(health) OVER (ORDER BY date)
  )
)
FROM liveness
WHERE date = '01-9-2022 UTC'
```

Returns:

```
                    dead_ranges
-----------------------------------------------------
("2022-01-12 15:27:22+00","2022-01-12 15:31:17+00")
```

## Arguments

The syntax is:

```sql theme={"dark"}
interpolate(
    agg HEARTBEATAGG,
    pred HEARTBEATAGG
) RETURNS HEARTBEATAGG
```

| Name | Type         | Default | Required | Description                                                              |
| ---- | ------------ | ------- | -------- | ------------------------------------------------------------------------ |
| agg  | HeartbeatAgg | -       | ✔        | A heartbeat aggregate containing liveness data for a particular interval |
| pred | HeartbeatAgg | -       |          | The heartbeat aggregate for the preceding interval, if one exists        |

## Returns

| Column      | Type         | Description                                                                                                |
| ----------- | ------------ | ---------------------------------------------------------------------------------------------------------- |
| interpolate | HeartbeatAgg | A copy of `agg` which has been update to include any heartbeat intervals extending past the end of `pred`. |

[toolkit-1.15.0]: https://github.com/timescale/timescaledb-toolkit/releases/tag/1.15.0