extendData for HeatMap

Dash Python
#1

I´m writting a live app that loads a large amount of data into a Heatmap. Currently I´m using the same method as in the examples.

app = dash.Dash()

app.layout = html.Div([
    dcc.Graph(
        id='live-update-graph',
        figure=initial_fig
    ),
    dcc.Interval(
        id='interval-component',
        interval=1*100, # in milliseconds
        n_intervals=0
    )
])

@app.callback(Output('live-update-graph', 'extendData'),
              Input('interval-component', 'n_intervals'))
def update_plot(n_interval):
    #parse data and load into dataframe
    #create the heatmap
    fig = go.Figure(data=go.Heatmap(
            z=df.values,
            x=df.columns,
            y=df.index,
            type='heatmap',
    ))
    return fig

app.run_server(debug=True, use_reloader=False)

I’m trying to achieve a real time heat map plot. The issue is that when I run the code, it’ll only plot the initial plot and not add any data and visualize it. Does anyone know how I could achieve this?

Thanks

#2

Could you update figure instead of the extendData property?

#3

Wouldn’t that require transferring all the data again?

#4

I’ve been able to update now with figure. The issue with this is that I can’t add to an existing plot (to my knowledge as I’m new to Dash) which leaves me constantly reloading a larger dataframe through each iteration from a large data set.

#5

Disclaimer: I’m new to Dash.

It was my understanding that extendData would allow me to append data to an existing plot. Am I wrong in thinking this?

#6

No, that is correct :slight_smile:

1 Like
#7

If the PlotlyJS graphing library supports updating heatmap data via extendTraces function call, then it should work with the extendData prop. This would be significantly faster than returning a new figure each interval.

@nqv also had a similar question in the recent past, which I just saw today. I haven’t looked in much detail; my primary use case remains scatter plot traces. I need to take a deeper look at heat maps.

Note: the extendData callback expects data to be formatted differently than with figure (or even figure.data). AFAIK you cannot use plotly.graph_objects with extendData