streams dont work when redim is applied on a source element later

[suvarchal]

it was bizzare to me that streams didnt work when redim.range was applied on a stream source Element later on, ie.., after defining the stream. I wonder if it can be called a bug or a feature request.

it can be reproduced with a change to last line in holoviews Tap example

%opts HeatMap [width=700 height=500 logz=True fontsize={'xticks': '6pt'}, tools=['hover'] xrotation=90] (cmap='RdBu_r') 
%opts Curve [width=375 height=500 yaxis='right'] (line_color='black') {+framewise}

df = pd.read_csv('http://assets.holoviews.org/data/diseases.csv.gz', compression='gzip')
dataset = hv.Dataset(df, vdims=('measles','Measles Incidence'))

heatmap = hv.HeatMap(dataset.aggregate(['Year', 'State'], np.mean),
                 label='Measles Incidence').select(Year=(1928, 2002))

posxy = hv.streams.Tap(source=heatmap, x=1951, y='New York')

def tap_histogram(x, y):
       return hv.Curve(dataset.select(State=y, Year=int(x)), kdims='Week',
               label='Year: %s, State: %s' % (x, y))
heatmap.redim.range(measles=(0,1)) + hv.DynamicMap(tap_histogram, kdims=[], streams=[posxy])  

on tap the Curve plot does not change, it would be nice addition if after defining the stream if we could still apply redim.

[philippjfr]

This definitely should work so I've marked this as a bug.

[suvarchal]

I wonder if it is because redim creates a clone of an Element which is not source anymore?

[philippjfr]

I wonder if it is because redim creates a clone of an Element which is not source anymore?

Right, it's something like that but we do have mechanisms to handle that kind of thing. Basically applying methods to a DynamicMap builds a graph, which can be traversed to find the sources, seems like in this case something is going wrong there.

[philippjfr]

Okay I just went through the example and looking at it again there is really no way this will ever work. HeatMap is a regular element so when you apply redim or indeed any other method you get a new object which is no longer linked to the stream. I would just make sure you apply redim before using the element as the source.

[jlstevens]

Right - that does make sense. In this case, we should have a warning in the docs to explain this behaviour. Generally methods like redim and clone generate new elements which means they won't refer to whatever was passed as source.

[suvarchal]

just to add not just heatmap any regular element like QuadMesh this would not work? may be a warning in documentation would avoid this pitfall.

[philippjfr]

So luckily I was completely wrong here, since 1.11.0 we now link objects with a shared _plot_id, which doesn't change unless the data is altered. Additionally, since #3478 we now inherit the plot_id on redim, which means the example above works just fine as is.