:orphan:
:html_theme.sidebar_secondary.remove:

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

.. _gallery_line_chart_with_datum:


Line Chart with Datum
---------------------------------
An example of using ``datum`` to highlight certain values, including a ``DateTime`` value.
This is adapted from two corresponding Vega-Lite Examples:
`Highlight a Specific Value <https://vega.github.io/vega-lite/docs/datum.html#highlight-a-specific-data-value>`_.


.. altair-plot::
    :remove-code:
    



    import altair as alt
    from vega_datasets import data

    source = data.stocks()

    lines = (
        alt.Chart(source)
        .mark_line()
        .encode(x="date", y="price", color="symbol")
    )

    xrule = (
        alt.Chart()
        .mark_rule(color="cyan", strokeWidth=2)
        .encode(x=alt.datum(alt.DateTime(year=2006, month="November")))
    )

    yrule = (
        alt.Chart().mark_rule(strokeDash=[12, 6], size=2).encode(y=alt.datum(350))
    )


    lines + yrule + xrule
    # No channel encoding options are specified in this chart
    # so the code is the same as for the method-based syntax.


.. tab-set::

    .. tab-item:: Method syntax
        :sync: method

        .. code:: python



            import altair as alt
            from vega_datasets import data

            source = data.stocks()

            lines = (
                alt.Chart(source)
                .mark_line()
                .encode(x="date", y="price", color="symbol")
            )

            xrule = (
                alt.Chart()
                .mark_rule(color="cyan", strokeWidth=2)
                .encode(x=alt.datum(alt.DateTime(year=2006, month="November")))
            )

            yrule = (
                alt.Chart().mark_rule(strokeDash=[12, 6], size=2).encode(y=alt.datum(350))
            )


            lines + yrule + xrule


    .. tab-item:: Attribute syntax
        :sync: attribute

        .. code:: python



            import altair as alt
            from vega_datasets import data

            source = data.stocks()

            lines = (
                alt.Chart(source)
                .mark_line()
                .encode(x="date", y="price", color="symbol")
            )

            xrule = (
                alt.Chart()
                .mark_rule(color="cyan", strokeWidth=2)
                .encode(x=alt.datum(alt.DateTime(year=2006, month="November")))
            )

            yrule = (
                alt.Chart().mark_rule(strokeDash=[12, 6], size=2).encode(y=alt.datum(350))
            )


            lines + yrule + xrule
            # No channel encoding options are specified in this chart
            # so the code is the same as for the method-based syntax.