docs-v2/content/flux/v0/stdlib/strings/isupper.md

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---
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))
```
{{< expand-wrapper >}}
{{% 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 |
{{% /expand %}}
{{< /expand-wrapper >}}