# Calculate the rate of change

This page documents an earlier version of InfluxDB.
InfluxDB v2 is the latest stable version.
See the equivalent **InfluxDB v2** documentation: Calculate the rate of change.

Use the `derivative()`

function
to calculate the rate of change between subsequent values or the
`aggregate.rate()`

function
to calculate the average rate of change per window of time.
If time between points varies, these functions normalize points to a common time interval
making values easily comparable.

## Rate of change between subsequent values

Use the `derivative()`

function
to calculate the rate of change per unit of time between subsequent *non-null* values.

```
data
|> derivative(unit: 1s)
```

By default, `derivative()`

returns only positive derivative values and replaces negative values with *null*.
Cacluated values are returned as floats.

**Given the following input:**

_time | _value |
---|---|

2020-01-01T00:00:00Z | 250 |

2020-01-01T00:04:00Z | 160 |

2020-01-01T00:12:00Z | 150 |

2020-01-01T00:19:00Z | 220 |

2020-01-01T00:32:00Z | 200 |

2020-01-01T00:51:00Z | 290 |

2020-01-01T01:00:00Z | 340 |

`derivative(unit: 1m)`

returns:

_time | _value |
---|---|

2020-01-01T00:04:00Z | |

2020-01-01T00:12:00Z | |

2020-01-01T00:19:00Z | 10.0 |

2020-01-01T00:32:00Z | |

2020-01-01T00:51:00Z | 4.74 |

2020-01-01T01:00:00Z | 5.56 |

Results represent the rate of change **per minute** between subsequent values with
negative values set to *null*.

### Return negative derivative values

To return negative derivative values, set the `nonNegative`

parameter to `false`

,

**Given the following input:**

_time | _value |
---|---|

2020-01-01T00:00:00Z | 250 |

2020-01-01T00:04:00Z | 160 |

2020-01-01T00:12:00Z | 150 |

2020-01-01T00:19:00Z | 220 |

2020-01-01T00:32:00Z | 200 |

2020-01-01T00:51:00Z | 290 |

2020-01-01T01:00:00Z | 340 |

**The following returns:**

```
|> derivative(
unit: 1m,
nonNegative: false
)
```

_time | _value |
---|---|

2020-01-01T00:04:00Z | -22.5 |

2020-01-01T00:12:00Z | -1.25 |

2020-01-01T00:19:00Z | 10.0 |

2020-01-01T00:32:00Z | -1.54 |

2020-01-01T00:51:00Z | 4.74 |

2020-01-01T01:00:00Z | 5.56 |

Results represent the rate of change **per minute** between subsequent values and
include negative values.

## Average rate of change per window of time

Use the `aggregate.rate()`

function
to calculate the average rate of change per window of time.

```
import "experimental/aggregate"
data
|> aggregate.rate(
every: 1m,
unit: 1s,
groupColumns: ["tag1", "tag2"]
)
```

`aggregate.rate()`

returns the average rate of change (as a float)
per `unit`

for time intervals defined by `every`

.
Negative values are replaced with *null*.

`aggregate.rate()`

does not support `nonNegative: false`

.

**Given the following input:**

_time | _value |
---|---|

2020-01-01T00:00:00Z | 250 |

2020-01-01T00:04:00Z | 160 |

2020-01-01T00:12:00Z | 150 |

2020-01-01T00:19:00Z | 220 |

2020-01-01T00:32:00Z | 200 |

2020-01-01T00:51:00Z | 290 |

2020-01-01T01:00:00Z | 340 |

**The following returns:**

```
|> aggregate.rate(
every: 20m,
unit: 1m
)
```

_time | _value |
---|---|

2020-01-01T00:20:00Z | |

2020-01-01T00:40:00Z | 10.0 |

2020-01-01T01:00:00Z | 4.74 |

2020-01-01T01:20:00Z | 5.56 |

Results represent the **average change rate per minute** of every **20 minute interval**
with negative values set to *null*.
Timestamps represent the right bound of the time window used to average values.

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