BUG - Decimator does not work with multiple traces

[AlexandreSajus]

The decimator should work with multiple traces in a line chart

Without decimator:

With decimator:

[2024-03-28 15:10:31][Taipy][INFO]  * Server starting on http://127.0.0.1:5000
C:\Users\asaju\Desktop\report_issues\venv\Lib\site-packages\taipy\gui\gui.py:635: TaipyGuiWarning: A problem occurred while resolving variable 'data' in module '__main__'.
  _warn(

Code:

from taipy.gui import Gui
from taipy.gui.data.decimator import MinMaxDecimator
import pandas as pd
import numpy as np

NOP = 500
decimator_instance = MinMaxDecimator(n_out=NOP)

data = pd.DataFrame(
    {
        "Time": np.arange(0, 10, 0.1),
        "A": np.arange(0, 10, 0.1) + np.random.randn(100) + 10,
        "B": np.arange(0, 10, 0.1) + np.random.randn(100),
    }
)

page = """
<|{data}|chart|x=Time|y[1]=A|y[2]=B|decimator=decimator_instance|>
"""

Gui(page).run()

[arcanaxion]

I believe you have to index the decimator property when you have multiple traces: https://docs.taipy.io/en/latest/manuals/gui/viselements/chart/#p-decimator

page = """
<|{data}|chart|x=Time|y[1]=A|y[2]=B|decimator[1]=decimator_instance|decimator[2]=decimator_instance|>
"""

[arcanaxion]

I initially couldn't get the decimator to work for your example even after the modification I made, and lowering NOP to 10. Seems like even when Decimator.threshold=None, there's still some threshold before the decimator kicks in. Maybe the devs can shed more light on this.

In the meantime, explicitly setting threshold to NOP seems to work:

from taipy.gui import Gui
from taipy.gui.data.decimator import MinMaxDecimator
import pandas as pd
import numpy as np

NOP = 10
decimator_instance = MinMaxDecimator(n_out=NOP, threshold=NOP)

data = pd.DataFrame(
    {
        "Time": np.arange(0, 10, 0.1),
        "A": np.arange(0, 10, 0.1) + np.random.randn(100) + 10,
        "B": np.arange(0, 10, 0.1) + np.random.randn(100),
    }
)

page = """
<|{data}|chart|x=Time|y[1]=A|y[2]=B|decimator[1]=decimator_instance|decimator[2]=decimator_instance|>
"""

Gui(page).run()

[AlexandreSajus]

Thanks finding the workaround, this does indeed seem to work properly. We should definitely still look at this, having to explicitely set the threshold does not make sense from the user's perspective

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