---
title: median() function
description: >
  `median()` returns the median `_value` of an input table or all non-null records
  in the input table with values that fall within the 0.5 quantile (50th percentile).
menu:
  flux_v0_ref:
    name: median
    parent: universe
    identifier: universe/median
weight: 101
flux/v0/tags: [transformations, aggregates, selectors]
introduced: 0.7.0
---

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`median()` returns the median `_value` of an input table or all non-null records
in the input table with values that fall within the 0.5 quantile (50th percentile).

### Function behavior
`median()` acts as an aggregate or selector transformation depending on the
specified `method`.

- **Aggregate**: When using the `estimate_tdigest` or `exact_mean` methods,
  `median()` acts as an aggregate transformation and outputs the average of
  non-null records with values that fall within the 0.5 quantile (50th percentile).
- **Selector**: When using the `exact_selector` method, `meidan()` acts as
  a selector selector transformation and outputs the non-null record with the
  value that represents the 0.5 quantile (50th percentile).

##### Function type signature

```js
(<-tables: stream[A], ?column: string, ?compression: float, ?method: string) => stream[A] where A: Record
```

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

## Parameters

### column

Column to use to compute the median. Default is `_value`.



### method

Computation method. Default is `estimate_tdigest`.

**Available methods**:
- **estimate_tdigest**: Aggregate method that uses a
[t-digest data structure](https://github.com/tdunning/t-digest) to
compute an accurate median estimate on large data sources.
- **exact_mean**: Aggregate method that takes the average of the two
points closest to the median value.
- **exact_selector**: Selector method that returns the row with the value
for which at least 50% of points are less than.

### compression

Number of centroids to use when compressing the dataset.
Default is `0.0`.

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

### tables

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




## Examples

- [Use median as an aggregate transformation](#use-median-as-an-aggregate-transformation)
- [Use median as a selector transformation](#use-median-as-a-selector-transformation)

### Use median as an aggregate transformation

```js
import "sampledata"

sampledata.float()
    |> median()

```

{{< 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 >}}

### Use median as a selector transformation

```js
import "sampledata"

sampledata.float()
    |> median(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 >}}