# GT.cols_label_with()
Relabel one or more columns using a function.
Usage
``` python
GT.cols_label_with(
columns=None,
fn=None,
)
```
The [cols_label_with()](GT.cols_label_with.md#great_tables.GT.cols_label_with) function allows for modification of column labels through a supplied function. By default, the function will be invoked on all column labels but this can be limited to a subset via the `columns` parameter.
## Parameters
`columns: SelectExpr = None`
The columns to target. Can either be a single column name or a series of column names provided in a list.
`fn: Callable[[str], str] | None = None`
A function that accepts a column name as input and returns a label as output.
## Returns
`GT`
The GT object is returned. This is the same object that the method is called on so that we can facilitate method chaining.
## Notes
GT always selects columns using their name in the underlying data. This means that a column's label is purely for final presentation.
## Examples
Let's use a subset of the [sp500](data.sp500.md#great_tables.data.sp500) dataset to create a gt table.
``` python
from great_tables import GT, md
from great_tables.data import sp500
gt = GT(sp500.head())
gt
```
| date | open | high | low | close | volume | adj_close |
|------------|-----------|-----------|---------|-----------|--------------|-----------|
| 2015-12-31 | 2060.5901 | 2062.54 | 2043.62 | 2043.9399 | 2655330000.0 | 2043.9399 |
| 2015-12-30 | 2077.3401 | 2077.3401 | 2061.97 | 2063.3601 | 2367430000.0 | 2063.3601 |
| 2015-12-29 | 2060.54 | 2081.5601 | 2060.54 | 2078.3601 | 2542000000.0 | 2078.3601 |
| 2015-12-28 | 2057.77 | 2057.77 | 2044.2 | 2056.5 | 2492510000.0 | 2056.5 |
| 2015-12-24 | 2063.52 | 2067.3601 | 2058.73 | 2060.99 | 1411860000.0 | 2060.99 |
We can pass `str.upper` to the `fn` parameter to convert all column labels to uppercase.
``` python
gt.cols_label_with(fn=str.upper)
```
| DATE | OPEN | HIGH | LOW | CLOSE | VOLUME | ADJ_CLOSE |
|------------|-----------|-----------|---------|-----------|--------------|-----------|
| 2015-12-31 | 2060.5901 | 2062.54 | 2043.62 | 2043.9399 | 2655330000.0 | 2043.9399 |
| 2015-12-30 | 2077.3401 | 2077.3401 | 2061.97 | 2063.3601 | 2367430000.0 | 2063.3601 |
| 2015-12-29 | 2060.54 | 2081.5601 | 2060.54 | 2078.3601 | 2542000000.0 | 2078.3601 |
| 2015-12-28 | 2057.77 | 2057.77 | 2044.2 | 2056.5 | 2492510000.0 | 2056.5 |
| 2015-12-24 | 2063.52 | 2067.3601 | 2058.73 | 2060.99 | 1411860000.0 | 2060.99 |
One useful use case is using [md()](md.md#great_tables.md), provided by **Great Tables**, to format column labels. For example, the following code demonstrates how to make the `date` and `adj_close` column labels bold using markdown syntax.
``` python
gt.cols_label_with(["date", "adj_close"], lambda x: md(f"**{x}**"))
```
| **date** | open | high | low | close | volume | **adj_close** |
|------------|-----------|-----------|---------|-----------|--------------|---------------|
| 2015-12-31 | 2060.5901 | 2062.54 | 2043.62 | 2043.9399 | 2655330000.0 | 2043.9399 |
| 2015-12-30 | 2077.3401 | 2077.3401 | 2061.97 | 2063.3601 | 2367430000.0 | 2063.3601 |
| 2015-12-29 | 2060.54 | 2081.5601 | 2060.54 | 2078.3601 | 2542000000.0 | 2078.3601 |
| 2015-12-28 | 2057.77 | 2057.77 | 2044.2 | 2056.5 | 2492510000.0 | 2056.5 |
| 2015-12-24 | 2063.52 | 2067.3601 | 2058.73 | 2060.99 | 1411860000.0 | 2060.99 |