Histogram
=========

A :doc:`Callable </Callables/Callable>` for generating a histogram.

Definition
----------

.. py:class:: controller.callable.outputter.Histogram(self, x: ColumnReference, title: str, x_axis_name: str, y_axis_name: str)

    :callable name: ``histogram``
    :callable type: :doc:`Outputter </Callables/Types/Outputter>`

    :param x: A column reference to find values for the x-axis. 
    :type x: ColumnReference
    :param title: The title of the chart.
    :type title: str
    :param x_axis_name: The name of the x-axis.
    :type x_axis_name: str
    :param y_axis_name: The name of the y-axis.
    :type y_axis_name: str

Parameters
----------

.. py:attribute:: x

    A column reference to find values for the x-axis. 

    :type: ColumnReference
    :required: True
    :choices: All columns in the target DataFrame

.. py:attribute:: title

    The title of the chart.

    :type: str
    :required: True

.. py:attribute:: x_axis_name

    The name of the x-axis.

    :type: str
    :required: True

.. py:attribute:: y_axis_name

    The name of the y-axis.

    :type: str
    :required: True

Output
------

A DataFrame is returned where it contains two columns matching the output conventions of an Outputter.

- The ``data`` column contains the generated histogram in PNG format.
- The ``type`` column indicates the data type to be ``image/png``.

Example configuration
---------------------

.. code-block:: javascript

    {
        "name": "foo",
        "callable": "histogram",
        "params": {
            "x": "$get_students_submissions.submission.score",
            "title": "Scores distribution",
            "x_axis_name": "Score",
            "y_axis_name": "Number of students"
        }
    }