---
title: cov() function
description: >
  `cov()` computes the covariance between two streams of tables.
menu:
  flux_v0_ref:
    name: cov
    parent: universe
    identifier: universe/cov
weight: 101
flux/v0/tags: [transformations, aggregates]
introduced: 0.7.0
---

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`cov()` computes the covariance between two streams of tables.



##### Function type signature

```js
(on: [string], x: A, y: B, ?pearsonr: bool) => stream[C] where C: Record
```

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

## Parameters

### x
({{< req >}})
First input stream.



### y
({{< req >}})
Second input stream.



### on
({{< req >}})
List of columns to join on.



### pearsonr

Normalize results to the Pearson R coefficient. Default is `false`.




## Examples

### Return the covariance between two streams of tables

```js
import "generate"

stream1 =
    generate.from(
        count: 5,
        fn: (n) => n * n,
        start: 2021-01-01T00:00:00Z,
        stop: 2021-01-01T00:01:00Z,
    )
        |> toFloat()

stream2 =
    generate.from(
        count: 5,
        fn: (n) => n * n * n / 2,
        start: 2021-01-01T00:00:00Z,
        stop: 2021-01-01T00:01:00Z,
    )
        |> toFloat()

cov(x: stream1, y: stream2, on: ["_time"])

```

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{{% expand "View example output" %}}

#### Output data

| _value  |
| ------- |
| 87.75   |

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