> ## Documentation Index
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> Use this file to discover all available pages before exploring further.

# gp_lttb()

> Downsample a time series using the Largest Triangle Three Buckets method, while preserving gaps in original data

<Icon icon="flask" /> Early access <Icon icon="tag" iconType="duotone" /> Since [1.11.0][toolkit-1.11.0]

Downsample your data with the [Largest Triangle Three Buckets algorithm][largest-triangle-three-buckets-algorithm], while preserving gaps in the underlying data. This method is a specialization of the [LTTB][lttb] algorithm.

## Samples

This example uses a table with raw data generated as a sine wave, and removes a day from the middle of the data. You can
use gap preserving LTTB to downsample the data while keeping the bounds of the missing region.

```sql theme={"dark"}
SET TIME ZONE 'UTC';
CREATE TABLE metrics(date TIMESTAMPTZ, reading DOUBLE PRECISION);
INSERT INTO metrics
SELECT
    '2020-1-1 UTC'::timestamptz + make_interval(hours=>foo),
    (5 + 5 * sin(foo / 24.0 * PI()))
    FROM generate_series(1,168) foo;
DELETE FROM metrics WHERE date BETWEEN '2020-1-4 UTC' AND '2020-1-5 UTC';

SELECT time, value
FROM unnest((
    SELECT toolkit_experimental.gp_lttb(date, reading, 8)
    FROM metrics))
```

```text theme={"dark"}
time                   |             value
-----------------------+-------------------
2020-01-01 01:00:00+00 | 5.652630961100257
2020-01-02 12:00:00+00 |                 0
2020-01-03 23:00:00+00 | 5.652630961100255
2020-01-05 01:00:00+00 | 5.652630961100259
2020-01-05 13:00:00+00 | 9.957224306869051
2020-01-06 12:00:00+00 |                 0
2020-01-07 10:00:00+00 |  9.82962913144534
2020-01-08 00:00:00+00 | 5.000000000000004
```

## Arguments

The syntax is:

```sql theme={"dark"}
gp_lttb(
  ts TIMESTAMPTZ,
  value DOUBLE PRECISION,
  [gapsize INTERVAL,]
  resolution INT
) RETURNS Timevector
```

| Name       | Type             | Default | Required | Description                                                                                              |
| ---------- | ---------------- | ------- | -------- | -------------------------------------------------------------------------------------------------------- |
| ts         | TIMESTAMPTZ      | -       | ✔        | Timestamps for each data point                                                                           |
| value      | DOUBLE PRECISION | -       | ✔        | The value at each timestamp                                                                              |
| gapsize    | INTERVAL         | -       |          | Minimum gap size to divide input on                                                                      |
| resolution | INT              | -       | ✔        | The approximate number of points to return. Determines the horizontal resolution of the resulting graph. |

## Returns

| Column   | Type       | Description                                                                                                                                                                                             |
| -------- | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| gp\_lttb | Timevector | An object representing a series of values occurring at set intervals from a starting time. It can be unpacked with `unnest`. For more information, see the documentation on [timevectors][timevectors]. |

[largest-triangle-three-buckets-algorithm]: https://github.com/sveinn-steinarsson/flot-downsample

[lttb]: /api-reference/timescaledb-toolkit/downsampling/lttb

[timevectors]: /api-reference/timescaledb-toolkit/timevector/

[toolkit-1.11.0]: https://github.com/timescale/timescaledb-toolkit/releases/tag/1.11.0