Make .selected a proper Bokeh model

[crashMOGWAI]

This seems to be a pain point with users, and I've stumbled into as well. Resetting the whole .selected dict seems to trigger updates in most simple cases, but reliability is finicky at best with more complex selection updates. @bryevdv Your idea, not mine.

Currently the only way to spoof this type of selection function is to create multiple grouped sources and manipulate the selection/nonselection attributes, or stack multiple sources and use the filters. It starts to get out of hand when dealing with larger data sets. Rather than dealing with multiple sources, a single data source paired with a callback that sets the .selected index based on a selection within that group, and reliable plot update trigger is preferred. @clairetang6 Maybe a CDSView extension concept, SelectFilter?

This standalone would select groups accordingly if .selected could detect an internal change and push an update trigger.

def mod_doc(doc):
    ''''''
    import numpy as np
    from bokeh.plotting import figure
    from bokeh.layouts import layout
    from bokeh.models import ColumnDataSource
    from bokeh.sampledata.iris import flowers
    from bokeh.palettes import Spectral6
    from bokeh.transform import factor_cmap
    
    source = ColumnDataSource(flowers)  
    plot_size_and_tools = {
        'plot_height': 500, 'plot_width': 500,
        'tools':['box_select','tap','reset', 'help']
        }
    p1 = figure(title="Proper .selected", **plot_size_and_tools)
    p1.circle(
        x='petal_length', y='petal_width', source=source,
        color=factor_cmap('species', palette=Spectral6[3:], 
                          factors=list(set(flowers.species))), size=10)
    
    def cb_change(attr,old,new):
        data = source.data.copy()
        selected = source.selected.copy()
        species = np.asarray(data['species'])
        idx = selected['1d']['indices']
        if len(idx) != 0:
            selected['1d']['indices'] = []
            species_sel = list(set(species[idx]))  
            for each in species_sel:
                idx = np.where(species == each)[0].tolist()
                selected['1d']['indices'].extend(idx)
            source.selected.update(selected)
            
    source.on_change('selected', cb_change)
    worksheet = layout([[p1]], sizing_mode='fixed')
    doc.add_root(worksheet)
    return doc

def main():
    '''''' 
    from tornado.ioloop import IOLoop
    from bokeh.document import Document
    from bokeh.application.handlers import FunctionHandler
    from bokeh.application import Application
    from bokeh.server.server import Server

    io_loop = IOLoop.current()    
    doc = Document()
    app = Application(FunctionHandler(mod_doc))
    server = Server({'/proper.selected': app}, io_loop=io_loop, port=0)
    server.start()
    io_loop.add_callback(server.show,'/proper.selected')
    io_loop.start()

if __name__ == '__main__':
    main()

[bryevdv]

This has definitely been discussed, and I think generally agreed upon. (I thought there was an issue already but I can't find it) The only main concern is finding a way to do it with as clean a deprecation path as possible, so that years worth of examples do not break overnight without warning.

Once @clairetang6 is back, she will be a good person to weigh in on this, as it intersects some of the work recently done of CDS views.