---
title: experimental.quantile() function
description: >
  `experimental.quantile()` returns non-null records with values in the `_value` column that
  fall within the specified quantile or represent the specified quantile.
menu:
  flux_v0_ref:
    name: experimental.quantile
    parent: experimental
    identifier: experimental/quantile
weight: 101
flux/v0/tags: [transformations, aggregates, selectors]
introduced: 0.107.0
---

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`experimental.quantile()` returns non-null records with values in the `_value` column that
fall within the specified quantile or represent the specified quantile.

The `_value` column must contain float values.

## Computation methods and behavior
`experimental.quantile()` behaves like an **aggregate function** or a
**selector function** depending on the `method` parameter.
The following computation methods are available:

##### estimate_tdigest
An aggregate method that uses a [t-digest data structure](https://github.com/tdunning/t-digest)
to compute an accurate quantile estimate on large data sources.
When used, `experimental.quantile()` outputs non-null records with values
that fall within the specified quantile.

##### exact_mean
An aggregate method that takes the average of the two points closest to the quantile value.
When used, `experimental.quantile()` outputs non-null records with values
that fall within the specified quantile.

##### exact_selector
A selector method that returns the data point for which at least `q` points are less than.
When used, `experimental.quantile()` outputs the non-null record with the
value that represents the specified quantile.

##### Function type signature

```js
(
    <-tables: stream[{A with _value: float}],
    q: float,
    ?compression: float,
    ?method: string,
) => stream[{A with _value: float}]
```

{{% caption %}}
For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}

## Parameters

### q
({{< req >}})
Quantile to compute (`[0 - 1]`).



### method

Computation method. Default is `estimate_tdigest`.

**Supported methods**:
- estimate_tdigest
- exact_mean
- exact_selector

### compression

Number of centroids to use when compressing the dataset.
Default is `1000.0`.

A larger number produces a more accurate result at the cost of increased
memory requirements.

### tables

Input data. Default is piped-forward data (`<-`).




## Examples

- [Return values in the 50th percentile of each input table](#return-values-in-the-50th-percentile-of-each-input-table)
- [Return a value representing the 50th percentile of each input table](#return-a-value-representing-the-50th-percentile-of-each-input-table)

### Return values in the 50th percentile of each input table

```js
import "experimental"
import "sampledata"

sampledata.float()
    |> experimental.quantile(q: 0.5)

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t1   | -2.18   |
| 2021-01-01T00:00:10Z | t1   | 10.92   |
| 2021-01-01T00:00:20Z | t1   | 7.35    |
| 2021-01-01T00:00:30Z | t1   | 17.53   |
| 2021-01-01T00:00:40Z | t1   | 15.23   |
| 2021-01-01T00:00:50Z | t1   | 4.43    |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t2   | 19.85   |
| 2021-01-01T00:00:10Z | t2   | 4.97    |
| 2021-01-01T00:00:20Z | t2   | -3.75   |
| 2021-01-01T00:00:30Z | t2   | 19.77   |
| 2021-01-01T00:00:40Z | t2   | 13.86   |
| 2021-01-01T00:00:50Z | t2   | 1.86    |


#### Output data

| *tag | _value  |
| ---- | ------- |
| t1   | 9.135   |

| *tag | _value  |
| ---- | ------- |
| t2   | 9.415   |

{{% /expand %}}
{{< /expand-wrapper >}}

### Return a value representing the 50th percentile of each input table

```js
import "experimental"
import "sampledata"

sampledata.float()
    |> experimental.quantile(q: 0.5, method: "exact_selector")

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t1   | -2.18   |
| 2021-01-01T00:00:10Z | t1   | 10.92   |
| 2021-01-01T00:00:20Z | t1   | 7.35    |
| 2021-01-01T00:00:30Z | t1   | 17.53   |
| 2021-01-01T00:00:40Z | t1   | 15.23   |
| 2021-01-01T00:00:50Z | t1   | 4.43    |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t2   | 19.85   |
| 2021-01-01T00:00:10Z | t2   | 4.97    |
| 2021-01-01T00:00:20Z | t2   | -3.75   |
| 2021-01-01T00:00:30Z | t2   | 19.77   |
| 2021-01-01T00:00:40Z | t2   | 13.86   |
| 2021-01-01T00:00:50Z | t2   | 1.86    |


#### Output data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:20Z | t1   | 7.35    |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:10Z | t2   | 4.97    |

{{% /expand %}}
{{< /expand-wrapper >}}