.. This document is auto-generated by the altair-gallery extension. Do not modify directly.

.. _gallery_multiline_tooltip:


Multi-Line Tooltip
==================
This example shows how you can use selections and layers to create a
tooltip-like behavior tied to the x position of the cursor.
If you are looking for more standard tooltips, it is recommended to use the
tooltip encoding channel as shown in the
`Scatter Plot With Tooltips <https://altair-viz.github.io/gallery/scatter_tooltips.html>`_
example.

The following example employs a little trick to isolate the x-position of the
cursor: we add some transparent points with only an x encoding (no y encoding)
and tie a *nearest* selection to these, tied to the "x" field.


.. altair-plot::
    :code-below:

    
    import altair as alt
    import pandas as pd
    import numpy as np

    np.random.seed(42)
    source = pd.DataFrame(np.cumsum(np.random.randn(100, 3), 0).round(2),
                        columns=['A', 'B', 'C'], index=pd.RangeIndex(100, name='x'))
    source = source.reset_index().melt('x', var_name='category', value_name='y')

    # Create a selection that chooses the nearest point & selects based on x-value
    nearest = alt.selection(type='single', nearest=True, on='mouseover',
                            fields=['x'], empty='none')

    # The basic line
    line = alt.Chart(source).mark_line(interpolate='basis').encode(
        x='x:Q',
        y='y:Q',
        color='category:N'
    )

    # Transparent selectors across the chart. This is what tells us
    # the x-value of the cursor
    selectors = alt.Chart(source).mark_point().encode(
        x='x:Q',
        opacity=alt.value(0),
    ).add_selection(
        nearest
    )

    # Draw points on the line, and highlight based on selection
    points = line.mark_point().encode(
        opacity=alt.condition(nearest, alt.value(1), alt.value(0))
    )

    # Draw text labels near the points, and highlight based on selection
    text = line.mark_text(align='left', dx=5, dy=-5).encode(
        text=alt.condition(nearest, 'y:Q', alt.value(' '))
    )

    # Draw a rule at the location of the selection
    rules = alt.Chart(source).mark_rule(color='gray').encode(
        x='x:Q',
    ).transform_filter(
        nearest
    )

    # Put the five layers into a chart and bind the data
    alt.layer(
        line, selectors, points, rules, text
    ).properties(
        width=600, height=300
    )


.. toctree::
   :hidden: