Hi,
I am having quite the time understanding change.emit(). See my example below to see the struggle. My example has one datasource. Two buttons do two different callbacks: one will change the ys column of the ColumnDataSource being used, and the other will alter a GroupFilter being applied via CDSView (to toggle between colours). The callback for the column change made sense to me - renderer.glyph.change.emit() was intuitive. However the view/filter took a lot of trial and error - and I think I fundamentally don’t understand a few things which is leading to my struggle. There is a whole lot of “I can make it work but don’t know why it works” going on.
So what I don’t understand:
ITEM 1 - source.change.emit() will update glyphs even if the source itself doesn’t change. In both ycb and ccb in my example, I found that just adding src.change.emit() would result in things “working”, even though (in my head) I’m not actually changing the source - I’m either changing the column the glyph is reading for its values (ycb) or the group name the filter is using (ccb)… in both cases the source doesn’t change… why does this work then?
ITEM 2 - finding the specific thing to put .change.emit() on for the filter was way harder for me than I thought it should be. See all my comments in the ccb callback… I tried a bunch of things… can someone explain why what I arrived at worked while the other attempts don’t?
from bokeh.models import MultiLine, ColumnDataSource, Button, CustomJS, CDSView, GroupFilter
from bokeh.plotting import figure,show
from bokeh.layouts import layout
data = {'xs':[[0,2,2,0],[3,4,4,3],[5,6,6,5],[8,10,10,8]]
,'ys1':[[0,0,2,2],[3,3,4,4],[5,5,6,6],[8,8,10,10]]
,'ys2':[[0,0,3,3],[6,6,3,3],[2,2,4,4],[7,7,11,11]]
,'c':['blue','green','blue','green']}
src = ColumnDataSource(data)
#fig
fig = figure()
glyph = MultiLine(xs='xs',ys='ys1',line_color='c')
view = CDSView(source=src,filters=[GroupFilter(column_name='c',group='blue')])
r = fig.add_glyph(src,glyph,view=view)
#button to change the y source - this works nicely and "makes sense" to me
ybtn = Button(label = 'ysource1')
ybcb = CustomJS(args=dict(r=r,ybtn=ybtn)
,code='''
if (ybtn.label == 'ysource1'){
ybtn.label = 'ysource2';
r.glyph.ys.field = 'ys2';
r.glyph.change.emit()
//THIS ALSO WORKS... BUT WHY:
//src.change.emit()
}
else if (ybtn.label == 'ysource2'){
ybtn.label = 'ysource1';
r.glyph.ys.field = 'ys1';
r.glyph.change.emit()}
''')
ybtn.js_on_click(ybcb)
#button to apply a cdsview filter for color.. the callback behaviour... is confusing to me.
cbtn = Button(label = 'blue')
ccb = CustomJS(args=dict(r=r,cbtn=cbtn,view=view,src=src)
,code='''
if (cbtn.label == 'blue'){
cbtn.label = 'green';
view.filters[0].group = 'green';
//SRC.CHANGE.EMIT() MAKES THIS WORK.. 1) WHY DOES IT WORK IF THE SOURCE ITSELF ISN'T CHANGING?
//src.change.emit()
//BUT HOW DO I EMIT ONLY THE FILTER UPDATE CHANGE?
// THINGS I TRIED
// view.properties.change.emit() // view.properties returns undefined
// view.change.emit() // get nothing
//view.filters[0].change.emit() // get nothing
//r.properties.view.filters.change.emit() // returns undefined
//r.change.emit() // does nothing
//r.glyph.change.emit() // does nothing
//IT LOOKS LIKE I HAVE TO EMIT THE CHANGE ON THE RENDERER'S VIEW'S FILTER...
// THIS WORKS AFTER MUCH TRIAL AND ERROR AND CONSOLE.LOG-ING EVERYTHING etc.
r.view.properties.filters.change.emit()
}
else if (cbtn.label == 'green'){
cbtn.label = 'blue';
view.filters[0].group = 'blue';
//SRC.CHANGE.EMIT MAKES THIS WORK
//src.change.emit();
// SAME THING THAT WORKS AS ABOVE...
r.view.properties.filters.change.emit()
}
''')
cbtn.js_on_click(ccb)
lo = layout([[fig,ybtn,cbtn]])
show(lo)
As always thank you so much for this library and ongoing support!
