Unexpected inverted y-axis from `FigureResampler`

[darynwhite]

First, thanks for creating this! Our data can be very oversized for Plotly and this has the potential to save us a lot of development time!

Background:
I'm developing a library of Plotly figure functions for our varying datatypes (meteorological and oceanographic) and our rain sensor samples at 1-minute intervals, but our data extend from 10 months to 2+ years.

Problem:
It's on the verge of perfect, but I cannot determine why the y-axis is inverting.
Here is the code that generates a standard Plotly Scattergl plot that will always crash a browser or notebook:

fig = plotly.graph_objects.Figure()
fig.add_trace(
    plotly.graph_objects.Scattergl(
        x=pt0.RAIN.data.index,
        y=pt0.RAIN.data.loc[:, IDX[1,"1046",'Vol']],
        mode="markers",
        showlegend=True,
        name="Rain Vol",
    )
)

And here is the code that I'm attempting to use to generate a Resampler figure:

fig = FigureResampler(plotly.graph_objects.Figure())
fig.add_trace(
    plotly.graph_objects.Scattergl(
        name="Rain Vol", 
        showlegend=True,
        mode="markers",
    ),
    hf_x=pt0.RAIN.data.index, 
    hf_y=pt0.RAIN.data.loc[:, IDX[1,"1046",'Vol']],
    downsampler=EveryNthPoint(interleave_gaps=False),
    max_n_samples=int(pt0.RAIN.data.index.size / 4),
    limit_to_view=True,
)

fig.show_dash(mode="inline")

[jvdd]

Hi @darynwhite,

Sounds like an awesome project!
Thanks for pointing out this issue :)

This is indeed unexpected / weird behavior. Plotly-Resampler should behave exactly the same as plotly.

I believe in your exanple plotly-resampler considers the datatype of hf_y as string (categorical) - as your y-axis is inverted and takes weird non-uniform steps.
Does it work as expected when you call .astype("float32") on the series that you pass as hf_y?.

Can you give me more details of the datatype of hf_y (and perhaps also hf_x)?
Giving a minimal reproducible example would be even more awesome!

Cheers, Jeroen

[jonasvdd]

Hi @darynwhite (@jvdd),

Thank you for submitting this issue!

I digged into it, and was able to reconstruct a minimal example of the undesired behavior.
The problem indeed is that your input hf_y data is of type object, which is cast to string by this code snippet below ⬇️

plotly-resampler/plotly_resampler/figure_resampler/figure_resampler_interface.py

Lines 677 to 682 in cc951c1

	# If the categorical or string-like hf_y data is of type object (happens
	# when y argument is used for the trace constructor instead of hf_y), we
	# transform it to type string as such it will be sent as categorical data
	# to the downsampling algorithm
	if hf_y.dtype == "object":
	hf_y = hf_y.astype("str")

But as this is diverging behavior from plotly w.r.t. numeric series of dtype object, I will fix this in a future PR!
Will create a release fix later this day!

[jonasvdd]

Is fixed in plotly-resampler 0.7.2.2

[darynwhite]

Well, that did fix it, and you were correct. Despite it being NaNs and float32 data, Pandas had it be of dtype: object.

Your suggestion of calling it with .astype("float32") worked before pulling the PyPi update, but the changes from #90 also fixed it.

Thanks! I look forward to integrating this into our workflows!