## 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       |