---
title: strings.isUpper() function
description: >
  `strings.isUpper()` tests if a single character string is uppercase.
menu:
  flux_v0_ref:
    name: strings.isUpper
    parent: strings
    identifier: strings/isUpper
weight: 101
---

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`strings.isUpper()` tests if a single character string is uppercase.



##### Function type signature

```js
(v: string) => bool
```

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

## Parameters

### v
({{< req >}})
Single-character string value to test.




## Examples

### Filter by columns with single-letter uppercase values

```js
import "strings"

data
    |> filter(fn: (r) => strings.isUpper(v: r._value))

```

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

#### Input data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2022-01-01T00:00:00Z | t1   | a       |
| 2022-01-01T00:01:00Z | t1   | B       |
| 2022-01-01T00:02:00Z | t1   | C       |
| 2022-01-01T00:03:00Z | t1   | d       |
| 2022-01-01T00:04:00Z | t1   | e       |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2022-01-01T00:00:00Z | t2   | F       |
| 2022-01-01T00:01:00Z | t2   | g       |
| 2022-01-01T00:02:00Z | t2   | H       |
| 2022-01-01T00:03:00Z | t2   | i       |
| 2022-01-01T00:04:00Z | t2   | J       |


#### Output data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2022-01-01T00:01:00Z | t1   | B       |
| 2022-01-01T00:02:00Z | t1   | C       |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2022-01-01T00:00:00Z | t2   | F       |
| 2022-01-01T00:02:00Z | t2   | H       |
| 2022-01-01T00:04:00Z | t2   | J       |

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