---
title: interpolate() | Tiger Data Docs
description: Adjust a heartbeat aggregate with predecessor information
---

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

```
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:

```
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`. |