---
title: experimental.diff() function
description: >
  `experimental.diff()` takes two table streams as input and produces a diff.
menu:
  flux_v0_ref:
    name: experimental.diff
    parent: experimental
    identifier: experimental/diff
weight: 101

introduced: 0.175.0
---

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`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}]
```

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

## Parameters

### want
({{< req >}})
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)

```

{{< expand-wrapper >}}
{{% expand "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       |

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

### 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)

```