---
title: math.isNaN() function
description: >
  `math.isNaN()` reports whether `f` is an IEEE 754 "not-a-number" value.
menu:
  flux_v0_ref:
    name: math.isNaN
    parent: math
    identifier: math/isNaN
weight: 101
---

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`math.isNaN()` reports whether `f` is an IEEE 754 "not-a-number" value.



##### Function type signature

```js
(f: float) => bool
```

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

## Parameters

### f
({{< req >}})
Value to operate on.




## Examples

- [Check if a value is a NaN float value](#check-if-a-value-is-a-nan-float-value)
- [Use math.isNaN in map](#use-mathisnan-in-map)

### Check if a value is a NaN float value

```js
import "math"

math.isNaN(f: 12.345)// false


```


### Use math.isNaN in map

```js
import "math"

data
    |> map(fn: (r) => ({r with _value: math.isNaN(f: r._value)}))

```

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{{% expand "View example input and output" %}}

#### Input data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t1   | -2.18   |
| 2021-01-01T00:00:10Z | t1   | NaN     |
| 2021-01-01T00:00:20Z | t1   | 7.35    |
| 2021-01-01T00:00:30Z | t1   | NaN     |
| 2021-01-01T00:00:40Z | t1   | NaN     |
| 2021-01-01T00:00:50Z | t1   | 4.43    |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t2   | NaN     |
| 2021-01-01T00:00:10Z | t2   | 4.97    |
| 2021-01-01T00:00:20Z | t2   | -3.75   |
| 2021-01-01T00:00:30Z | t2   | 19.77   |
| 2021-01-01T00:00:40Z | t2   | NaN     |
| 2021-01-01T00:00:50Z | t2   | 1.86    |


#### Output data

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

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

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