---
title: relativeStrengthIndex() function
description: >
  `relativeStrengthIndex()` measures the relative speed and change of values in input tables.
menu:
  flux_v0_ref:
    name: relativeStrengthIndex
    parent: universe
    identifier: universe/relativeStrengthIndex
weight: 101
flux/v0/tags: [transformations]
introduced: 0.38.0
---

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`relativeStrengthIndex()` measures the relative speed and change of values in input tables.

### Relative strength index (RSI) rules
- The general equation for calculating a relative strength index (RSI) is
  `RSI = 100 - (100 / (1 + (AVG GAIN / AVG LOSS)))`.
- For the first value of the RSI, `AVG GAIN` and `AVG LOSS` are averages of the `n` period.
- For subsequent calculations:
  - `AVG GAIN` = `((PREVIOUS AVG GAIN) * (n - 1)) / n`
  - `AVG LOSS` = `((PREVIOUS AVG LOSS) * (n - 1)) / n`
- `relativeStrengthIndex()` ignores `null` values.

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

##### Function type signature

```js
(<-tables: stream[A], n: int, ?columns: [string]) => stream[B] where A: Record, B: Record
```

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

### n
({{< req >}})
Number of values to use to calculate the RSI.



### columns

Columns to operate on. Default is `["_value"]`.



### tables

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




## Examples

### Calculate a three point relative strength index

```js
import "sampledata"

sampledata.int()
    |> relativeStrengthIndex(n: 3)

```

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#### 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 |
| -------------------- | ------------------ | ---- |
| 2021-01-01T00:00:30Z | 84.375             | t1   |
| 2021-01-01T00:00:40Z | 73.97260273972603  | t1   |
| 2021-01-01T00:00:50Z | 36.672325976230894 | t1   |

| _time                | _value            | *tag |
| -------------------- | ----------------- | ---- |
| 2021-01-01T00:00:30Z | 70.27027027027026 | t2   |
| 2021-01-01T00:00:40Z | 59.42857142857142 | t2   |
| 2021-01-01T00:00:50Z | 40.625            | t2   |

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