---
title: difference() function
description: >
  `difference()` returns the difference between subsequent values.
menu:
  flux_v0_ref:
    name: difference
    parent: universe
    identifier: universe/difference
weight: 101
flux/v0/tags: [transformations]
introduced: 0.7.1
---

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`difference()` returns the difference between subsequent values.

### Subtraction rules for numeric types
- The difference between two non-null values is their algebraic difference;
  or `null`, if the result is negative and `nonNegative: true`;
- `null` minus some value is always `null`;
- Some value `v` minus `null` is `v` minus the last non-null value seen
  before `v`; or `null` if `v` is the first non-null value seen.
- If `nonNegative` and `initialZero` are set to `true`, `difference()`
  returns the difference between `0` and the subsequent value.
  If the subsequent value is less than zero, `difference()` returns `null`.

### Output tables
For each input table with `n` rows, `difference()` outputs a table with
`n - 1` rows.

##### Function type signature

```js
(
    <-tables: stream[A],
    ?columns: [string],
    ?initialZero: bool,
    ?keepFirst: bool,
    ?nonNegative: bool,
) => stream[B] where A: Record, B: Record
```

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

## Parameters

### nonNegative

Disallow negative differences. Default is `false`.

When `true`, if a value is less than the previous value, the function
assumes the previous value should have been a zero.

### columns

List of columns to operate on. Default is `["_value"]`.



### keepFirst

Keep the first row in each input table. Default is `false`.

If `true`, the difference of the first row of each output table is null.

### initialZero

Use zero (0) as the initial value in the difference calculation
when the subsequent value is less than the previous value and `nonNegative` is
`true`. Default is `false`.



### tables

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




## Examples

- [Calculate the difference between subsequent values](#calculate-the-difference-between-subsequent-values)
- [Calculate the non-negative difference between subsequent values](#calculate-the-non-negative-difference-between-subsequent-values)
- [Calculate the difference between subsequent values with null values](#calculate-the-difference-between-subsequent-values-with-null-values)
- [Keep the first value when calculating the difference between values](#keep-the-first-value-when-calculating-the-difference-between-values)

### Calculate the difference between subsequent values

```js
import "sampledata"

sampledata.int()
    |> difference()

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 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   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

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


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 12      | t1   |
| 2021-01-01T00:00:20Z | -3      | t1   |
| 2021-01-01T00:00:30Z | 10      | t1   |
| 2021-01-01T00:00:40Z | -2      | t1   |
| 2021-01-01T00:00:50Z | -11     | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | -15     | t2   |
| 2021-01-01T00:00:20Z | -7      | t2   |
| 2021-01-01T00:00:30Z | 22      | t2   |
| 2021-01-01T00:00:40Z | -6      | t2   |
| 2021-01-01T00:00:50Z | -12     | t2   |

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

### Calculate the non-negative difference between subsequent values

```js
import "sampledata"

sampledata.int()
    |> difference(nonNegative: true)

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 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   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

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


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z | 12      | t1   |
| 2021-01-01T00:00:20Z |         | t1   |
| 2021-01-01T00:00:30Z | 10      | t1   |
| 2021-01-01T00:00:40Z |         | t1   |
| 2021-01-01T00:00:50Z |         | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z |         | t2   |
| 2021-01-01T00:00:20Z |         | t2   |
| 2021-01-01T00:00:30Z | 22      | t2   |
| 2021-01-01T00:00:40Z |         | t2   |
| 2021-01-01T00:00:50Z |         | t2   |

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

### Calculate the difference between subsequent values with null values

```js
import "sampledata"

sampledata.int(includeNull: true)
    |> difference()

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

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

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


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z |         | t1   |
| 2021-01-01T00:00:20Z | 9       | t1   |
| 2021-01-01T00:00:30Z |         | t1   |
| 2021-01-01T00:00:40Z |         | t1   |
| 2021-01-01T00:00:50Z | -3      | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:10Z |         | t2   |
| 2021-01-01T00:00:20Z | -7      | t2   |
| 2021-01-01T00:00:30Z | 22      | t2   |
| 2021-01-01T00:00:40Z |         | t2   |
| 2021-01-01T00:00:50Z | -18     | t2   |

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

### Keep the first value when calculating the difference between values

```js
import "sampledata"

sampledata.int()
    |> difference(keepFirst: true)

```

{{< expand-wrapper >}}
{{% expand "View example input and output" %}}

#### Input data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 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   |
| 2021-01-01T00:00:40Z | 15      | t1   |
| 2021-01-01T00:00:50Z | 4       | t1   |

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


#### Output data

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z |         | t1   |
| 2021-01-01T00:00:10Z | 12      | t1   |
| 2021-01-01T00:00:20Z | -3      | t1   |
| 2021-01-01T00:00:30Z | 10      | t1   |
| 2021-01-01T00:00:40Z | -2      | t1   |
| 2021-01-01T00:00:50Z | -11     | t1   |

| _time                | _value  | *tag |
| -------------------- | ------- | ---- |
| 2021-01-01T00:00:00Z |         | t2   |
| 2021-01-01T00:00:10Z | -15     | t2   |
| 2021-01-01T00:00:20Z | -7      | t2   |
| 2021-01-01T00:00:30Z | 22      | t2   |
| 2021-01-01T00:00:40Z | -6      | t2   |
| 2021-01-01T00:00:50Z | -12     | t2   |

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