Slider bar in altair interactive plot with wrong front and initial placement

Question

I have this interactive plot with a slider bar over the 'Time' field. My problems are:

• The font is different from the other texts in the plot (both with Chrome and Edge). I looked at the doc but I could not find a way to change it. Is it possible?
• I cannot set the init attribute of the slider properly. Following the example doc I try to set init={'Time': 3} (I need it to be at the end), but I get the following error

    selector = alt.selection_single(
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\vegalite\v5\api.py", line 395, in selection_single
    return selection(type="point", **kwargs)
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\vegalite\v5\api.py", line 365, in selection
    return parameter(select=select, **param_kwds)
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\vegalite\v5\api.py", line 319, in parameter
    parameter.param = core.SelectionParameter(
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\vegalite\v5\schema\core.py", line 14283, in __init__
    super(SelectionParameter, self).__init__(name=name, select=select, bind=bind, value=value,
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\utils\schemapi.py", line 177, in __init__
    self.to_dict(validate=True)
  File "C:\Users\sparisi\Anaconda3\lib\site-packages\altair\utils\schemapi.py", line 340, in to_dict
    raise SchemaValidationError(self, err)
altair.utils.schemapi.SchemaValidationError: Invalid specification

        altair.vegalite.v5.schema.core.SelectionParameter->0, validating 'type'

        3 is not of type 'array'

Answer 1

Since you are a bit ahead of the curve (since you are on vegalite V5 already), you can use the upcoming parameter for interactivity in Altair. See here for some examples https://christopherdavisuci.github.io/UCI-Math-10/param.html

Especially the transform-filter section is relevant for you.

Here you see the init is replaced with a value parameter.

Regarding the init error you observe. I cannot reproduce this using the example you refer to (see this colab notebook), so I suspect something else is wrong. If you prepare a minimum reproducible example I can have a look again.

Regarding the font of the sliders. There is no known syntax in altair for doing this, but if it is important for you, you can overrule the css. See this SO answer for an example https://stackoverflow.com/a/62104504/2459096