---
title: experimental.diff() function
description: experimental.diff() takes two table streams as input and produces a diff.
url: https://docs.influxdata.com/flux/v0/stdlib/experimental/diff/
estimated_tokens: 2089
product: Flux
version: v0
---

# experimental.diff() function

-   Flux 0.175.0+
-   View InfluxDB support

`experimental.diff()` is [subject to change at any time](/flux/v0/stdlib/experimental/#experimental-packages-are-subject-to-change).

`experimental.diff()` takes two table streams as input and produces a diff.

`experimental.diff()` compares tables with the same group key. If compared tables are different, the function returns a table for that group key with one or more rows. If there are no differences, the function does not return a table for that group key.

**Note:** `experimental.diff()` cannot tell the difference between an empty table and a non-existent table.

**Important:** The output format of the diff is not considered stable and the algorithm used to produce the diff may change. The only guarantees are those mentioned above.

##### Function type signature

```js
(<-got: stream[A], want: stream[A]) => stream[{A with _diff: string}]
```

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

## Parameters

### want

(Required) Input stream for the `-` side of the diff.

### got

Input stream for the `+` side of the diff.

## Examples

-   [Output a diff between two streams of tables](#output-a-diff-between-two-streams-of-tables)
-   [Return a diff between a stream of tables and the expected output](#return-a-diff-between-a-stream-of-tables-and-the-expected-output)

### Output a diff between two streams of tables

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

want = sampledata.int()
got =
    sampledata.int()
        |> map(fn: (r) => ({r with _value: if r._value > 15 then r._value + 1 else r._value}))

experimental.diff(got: got, want: want)
```

[](#view-example-input)

View example input

#### Input data

| _diff | *tag | _time | _value |
| --- | --- | --- | --- |
|  | t1 | 2021-01-01T00:00:00Z | -2 |
|  | t1 | 2021-01-01T00:00:10Z | 10 |
|  | t1 | 2021-01-01T00:00:20Z | 7 |
| - | t1 | 2021-01-01T00:00:30Z | 17 |
| + | t1 | 2021-01-01T00:00:30Z | 18 |
|  | t1 | 2021-01-01T00:00:40Z | 15 |
|  | t1 | 2021-01-01T00:00:50Z | 4 |

| _diff | *tag | _time | _value |
| --- | --- | --- | --- |
| - | t2 | 2021-01-01T00:00:00Z | 19 |
| + | t2 | 2021-01-01T00:00:00Z | 20 |
|  | t2 | 2021-01-01T00:00:10Z | 4 |
|  | t2 | 2021-01-01T00:00:20Z | -3 |
| - | t2 | 2021-01-01T00:00:30Z | 19 |
| + | t2 | 2021-01-01T00:00:30Z | 20 |
|  | t2 | 2021-01-01T00:00:40Z | 13 |
|  | t2 | 2021-01-01T00:00:50Z | 1 |

### Return a diff between a stream of tables and the expected output

```js
import "experimental"

want = from(bucket: "backup-example-bucket") |> range(start: -5m)

from(bucket: "example-bucket")
    |> range(start: -5m)
    |> experimental.diff(want: want)
```