---
title: experimental.stddev() function
description: >
  `experimental.stddev()` returns the standard deviation of non-null values in the `_value`
  column for each input table.
menu:
  flux_v0_ref:
    name: experimental.stddev
    parent: experimental
    identifier: experimental/stddev
weight: 101
flux/v0/tags: [transformations, aggregates]
introduced: 0.107.0
---

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`experimental.stddev()` returns the standard deviation of non-null values in the `_value`
column for each input table.

## Standard deviation modes
The following modes are available when calculating the standard deviation of data.

##### sample
Calculate the sample standard deviation where the data is considered to be
part of a larger population.

##### population
Calculate the population standard deviation where the data is considered a
population of its own.

##### Function type signature

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

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

## Parameters

### mode

Standard deviation mode or type of standard deviation to calculate.
Default is `sample`.

**Available options**:
- sample
- population

### tables

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




## Examples

### Return the standard deviation in input tables

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

sampledata.float()
    |> experimental.stddev()

```

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{{% 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   | 7.263244454099008 |

| *tag | _value           |
| ---- | ---------------- |
| t2   | 9.85926704510364 |

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