Hello! I have already created a topic about heatmap live update.
To recap: I have a dataframe that updates at a rate of a few milliseconds. I would like heatmap to display this data and update every few seconds. However, the program doesn’t work correctly and after a while I get an error Callback error updating heatmap.figure.
Initially I assumed I had written the code for the dash app wrong, but I don’t think there are any mistakes in it. Therefore, I have a question: Can this happen because the dataframe itself is updating outside of the dash app? Here is my implementation:
- I initially start the server with the app. At this stage data.raw_frame is empty.
# initialise dataframe and figure
fig = go.Figure(data=go.Heatmap(z=[],x=[],y=[]))
fig.update_xaxes(range=[data.x_min,data.x_max])
fig.update_yaxes(range=[data.y_min,data.y_max])
# Build App
app = JupyterDash(__name__)
app.layout = html.Div(
[
dcc.Graph(id="heatmap", figure=fig),
dcc.Interval(id="animateInterval", interval=3*1000, n_intervals=0),
],
)
@app.callback(
Output("heatmap", "figure"),
Input("animateInterval", "n_intervals"),
)
def doUpdate(i):
df = data.raw_frame.copy()
z_val = df.heat_value
x_val = df.x_value
y_val = df.y_value
return go.Figure(fig).update_traces(go.Heatmap(z=z_val,
x=x_val,
y=y_val))
app.run_server(mode="external", port=8051, debug=True)
- Then (in another jupyter cell) I run code that fills my dataframe within the given limits. Let it be filled with random numbers for simplicity
data.iter_setup()
for i in range(len(data.load)):
data.write(load = data.load[i],
frequency = data.frequency[i],
response = np.random.rand())
time.sleep(0.0001)
Thus, every iteration new values are added to the data.raw_frame, and every few seconds the App accesses this dataframe and builds a heatmap based on it. That’s why I thought, maybe the error is caused by the fact, that the dataframe is updated outside the APP?
At first I thought there couldn’t be a problem with this, since, if I understand correctly, Dash uses multithreading and it can’t be a problem for it to access any variables in the whole jupyter notebook. I would like to get your feedback on this issue.
Thank you!