Field Selection?

[jomar0]

Hi,
I'm trying to create a drop-down selector that allows the user to change the field encoded as colour on a choropleth map, however I am struggling to find any resources that show this. Is it even possible? How would I do it?

Also, I get a Schema Validation Error when creating the selector, using similar dropdown filter code as this example. Here is my code and output (metrics is a standard python list):

metric_dropdown = alt.binding_select(options=metrics)
metric_select = alt.selection_single(bind=metric_dropdown, name='Metric')

---------------------------------------------------------------------------
SchemaValidationError                     Traceback (most recent call last)
Cell In [139], line 1
----> 1 metric_dropdown = alt.binding_select(options=metrics, type="Q")
      2 metric_select = alt.selection_single(bind=metric_dropdown, name='Metric')

File c:\scripts\Python310\lib\site-packages\altair\vegalite\v4\api.py:280, in binding_select(**kwargs)
    277 @utils.use_signature(core.BindRadioSelect)
    278 def binding_select(**kwargs):
    279     """A select binding"""
--> 280     return core.BindRadioSelect(input="select", **kwargs)

File c:\scripts\Python310\lib\site-packages\altair\vegalite\v4\schema\core.py:1769, in BindRadioSelect.__init__(self, input, options, debounce, element, labels, name, type, **kwds)
   1767 def __init__(self, input=Undefined, options=Undefined, debounce=Undefined, element=Undefined,
   1768              labels=Undefined, name=Undefined, type=Undefined, **kwds):
-> 1769     super(BindRadioSelect, self).__init__(input=input, options=options, debounce=debounce,
   1770                                           element=element, labels=labels, name=name, type=type,
   1771                                           **kwds)

File c:\scripts\Python310\lib\site-packages\altair\vegalite\v4\schema\core.py:1712, in Binding.__init__(self, *args, **kwds)
   1711 def __init__(self, *args, **kwds):
-> 1712     super(Binding, self).__init__(*args, **kwds)

File c:\scripts\Python310\lib\site-packages\altair\utils\schemapi.py:177, in SchemaBase.__init__(self, *args, **kwds)
    174 object.__setattr__(self, "_kwds", kwds)
    176 if DEBUG_MODE and self._class_is_valid_at_instantiation:
--> 177     self.to_dict(validate=True)

File c:\scripts\Python310\lib\site-packages\altair\utils\schemapi.py:340, in SchemaBase.to_dict(self, validate, ignore, context)
    338         self.validate(result)
    339     except jsonschema.ValidationError as err:
--> 340         raise SchemaValidationError(self, err)
    341 return result

SchemaValidationError: Invalid specification

        altair.vegalite.v4.schema.core.BindRadioSelect->options, validating 'type'

        None is not of type 'array'

[joelostblom]

You can see an example of this at the bottom of this page in the next version of the docs (the example using transform_fold). It is originally from this issue vega/vega-lite#7264 which sounds like what you want to do