> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/marimo-team/marimo/llms.txt
> Use this file to discover all available pages before exploring further.

# altair_chart

Make reactive charts with Altair.

## Usage

```python theme={null}
import altair as alt
import marimo as mo
from vega_datasets import data

chart = (
    alt.Chart(data.cars())
    .mark_point()
    .encode(
        x="Horsepower",
        y="Miles_per_Gallon",
        color="Origin",
    )
)

chart = mo.ui.altair_chart(chart)
```

```python theme={null}
# View the chart and selected data as a dataframe
mo.hstack([chart, chart.value])
```

## Signature

```python theme={null}
mo.ui.altair_chart(
    chart: altair.Chart,
    chart_selection: Literal["point"] | Literal["interval"] | bool = True,
    legend_selection: list[str] | bool = True,
    *,
    label: str = "",
    on_change: Optional[Callable[[ChartDataType], None]] = None
)
```

## Parameters

<ParamField path="chart" type="altair.Chart" required>
  An Altair Chart object.
</ParamField>

<ParamField path="chart_selection" type="Literal['point'] | Literal['interval'] | bool" default="True">
  Selection type: `"point"`, `"interval"`, or a bool. Defaults to `True` which will automatically detect the best selection type. This is ignored if the chart already has a point/interval selection param.
</ParamField>

<ParamField path="legend_selection" type="list[str] | bool" default="True">
  List of legend fields (columns) for which to enable selection, `True` to enable selection for all fields, or `False` to disable selection entirely. This is ignored if the chart already has a legend selection param.
</ParamField>

<ParamField path="label" type="str" default="">
  Markdown label for the element.
</ParamField>

<ParamField path="on_change" type="Optional[Callable[[ChartDataType], None]]" default="None">
  Optional callback to run when this element's value changes.
</ParamField>

## Attributes

<ParamField path="value" type="ChartDataType">
  A dataframe of the plot data filtered by the selections.
</ParamField>

<ParamField path="dataframe" type="ChartDataType">
  A dataframe of the unfiltered chart data.
</ParamField>

<ParamField path="selections" type="ChartSelection">
  The selection of the chart; this may be an interval along the name of an axis or a selection of points.
</ParamField>

## Methods

### apply\_selection

Apply the selection to a DataFrame.

This method is useful when you have a layered chart and you want to apply the selection to a DataFrame.

```python theme={null}
selected_df = chart.apply_selection(cars)
```

**Parameters:**

* `df` (ChartDataType): A DataFrame to apply the selection to.

**Returns:** ChartDataType - A DataFrame of the plot data filtered by the selections.