Step plot not working with resample_when

[ribas591]

ALL software version info

Software Version Info: short

hvplot 0.12.2
python 3.12.12
marimo  0.19.6

firefox
linux

Software Version Info: full

Package            Version
------------------ -----------
anyio              4.12.1
bleach             6.3.0
bokeh              3.8.2
certifi            2026.1.4
charset-normalizer 3.4.4
click              8.3.1
colorcet           3.1.0
contourpy          1.3.3
docutils           0.22.4
h11                0.16.0
holoviews          1.22.1
hvplot             0.12.2
idna               3.11
itsdangerous       2.2.0
jedi               0.19.2
jinja2             3.1.6
linkify-it-py      2.0.3
loro               1.10.3
marimo             0.19.6
markdown           3.10.1
markdown-it-py     4.0.0
markupsafe         3.0.3
mdit-py-plugins    0.5.0
mdurl              0.1.2
msgspec            0.20.0
narwhals           2.15.0
numpy              2.4.1
packaging          26.0
pandas             3.0.0
panel              1.8.6
param              2.3.1
parso              0.8.5
pillow             12.1.0
psutil             7.2.1
pyarrow            23.0.0
pygments           2.19.2
pymdown-extensions 10.20.1
python-dateutil    2.9.0.post0
pyviz-comms        3.0.6
pyyaml             6.0.3
requests           2.32.5
six                1.17.0
starlette          0.52.1
tomlkit            0.14.0
tornado            6.5.4
tqdm               4.67.1
typing-extensions  4.15.0
uc-micro-py        1.0.3
urllib3            2.6.3
uvicorn            0.40.0
webencodings       0.5.1
websockets         16.0
xyzservices        2025.11.0

Description of expected behavior and the observed behavior

Thank you very much for this excellent library!

I am trying to plot a large time series with hvplot. Therefore, I have to use downsampling. I was very happy to find the "resample_when" option, which was just what I needed.
Line plots work well. However, problems arise when I try to use step plots.

Complete, minimal, self-contained example code that reproduces the issue

import hvplot.pandas  # noqa
import pandas as pd

df = pd.read_parquet("https://datasets.holoviz.org/sensor/v1/data.parq")

# works fine
df.hvplot.line(
        x="time",
        y="value",
        downsample=True,
        resample_when=1_000,
)

# also works
df.hvplot.step(
        x="time",
        y="value",
        where="post",
        downsample=True,
)

# error
df.hvplot.step(
        x="time",
        y="value",
        where="post",
        downsample=True,
        resample_when=1_000,
)

Stack traceback and/or browser JavaScript console output

ValueError: negative dimensions are not allowed

Traceback (most recent call last):
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/marimo/_output/formatters/holoviews_formatters.py", line 44, in _show_chart
    return from_panel(plot)._mime_()
           ^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/marimo/_plugins/ui/_impl/from_panel.py", line 285, in __init__
    ref, docs_json, render_json = render_component(self.obj)
                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/marimo/_plugins/ui/_impl/from_panel.py", line 164, in render_component
    root = obj._render_model(doc, comm)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/viewable.py", line 768, in _render_model
    model = self.get_root(doc, comm)
            ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/layout/base.py", line 329, in get_root
    root = super().get_root(doc, comm, preprocess)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/viewable.py", line 698, in get_root
    root = self._get_model(doc, comm=comm)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/layout/base.py", line 313, in _get_model
    objects, _ = self._get_objects(model, [], doc, root, comm)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/layout/base.py", line 295, in _get_objects
    child = pane._get_model(doc, root, model, comm)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/pane/holoviews.py", line 487, in _get_model
    plot = self._render(doc, comm, root)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/panel/pane/holoviews.py", line 581, in _render
    return renderer.get_plot(self.object, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/renderer.py", line 70, in get_plot
    plot = super().get_plot(obj, doc, renderer, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/renderer.py", line 239, in get_plot
    plot.update(init_key)
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/plot.py", line 958, in update
    return self.initialize_plot()
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 3474, in initialize_plot
    child = subplot.initialize_plot(ranges, plot, plots)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 2220, in initialize_plot
    self._init_glyphs(plot, element, ranges, source)
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 2120, in _init_glyphs
    data, mapping, style = self.get_data(element, ranges, style)
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/chart.py", line 466, in get_data
    element = interpolate_curve(element, interpolation=self.interpolation)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/param/parameterized.py", line 5948, in __new__
    return inst.__call__(*args,**params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 218, in __call__
    return element.apply(self, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/accessors.py", line 43, in pipelined_call
    result = __call__(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/accessors.py", line 200, in __call__
    new_obj = apply_function(self._obj, **inner_kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 212, in __call__
    return self._apply(element)
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 141, in _apply
    ret = self._process(element, key)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1142, in _process
    return element.map(self._process_layer, Element)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/data/__init__.py", line 204, in pipelined_fn
    result = method_fn(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/data/__init__.py", line 1316, in map
    return super().map(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/dimension.py", line 761, in map
    return map_fn(self) if applies else self
           ^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1136, in _process_layer
    xs, dvals = INTERPOLATE_FUNCS[self.p.interpolation](x, dvals)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1110, in pts_to_poststep
    steps = np.zeros(2 * len(x) - 1)
            ^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: negative dimensions are not allowed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/marimo/_output/formatting.py", line 237, in try_format
    mimetype, data = formatter(obj)
                     ^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/marimo/_output/formatters/holoviews_formatters.py", line 47, in _show_chart
    backend_output = hv.render(plot)
                     ^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/util/__init__.py", line 892, in render
    return renderer_obj.get_plot_state(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/renderer.py", line 273, in get_plot_state
    obj = self_or_cls.get_plot(obj=obj, renderer=renderer, **kwargs)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/renderer.py", line 70, in get_plot
    plot = super().get_plot(obj, doc, renderer, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/renderer.py", line 239, in get_plot
    plot.update(init_key)
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/plot.py", line 958, in update
    return self.initialize_plot()
           ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 3474, in initialize_plot
    child = subplot.initialize_plot(ranges, plot, plots)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 2220, in initialize_plot
    self._init_glyphs(plot, element, ranges, source)
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 2120, in _init_glyphs
    data, mapping, style = self.get_data(element, ranges, style)
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/chart.py", line 466, in get_data
    element = interpolate_curve(element, interpolation=self.interpolation)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/param/parameterized.py", line 5948, in __new__
    return inst.__call__(*args,**params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 218, in __call__
    return element.apply(self, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/accessors.py", line 43, in pipelined_call
    result = __call__(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/accessors.py", line 200, in __call__
    new_obj = apply_function(self._obj, **inner_kwargs)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 212, in __call__
    return self._apply(element)
           ^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/operation.py", line 141, in _apply
    ret = self._process(element, key)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1142, in _process
    return element.map(self._process_layer, Element)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/data/__init__.py", line 204, in pipelined_fn
    result = method_fn(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/data/__init__.py", line 1316, in map
    return super().map(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/core/dimension.py", line 761, in map
    return map_fn(self) if applies else self
           ^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1136, in _process_layer
    xs, dvals = INTERPOLATE_FUNCS[self.p.interpolation](x, dvals)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ar/Work/hvplot_test/.venv/lib/python3.12/site-packages/holoviews/operation/element.py", line 1110, in pts_to_poststep
    steps = np.zeros(2 * len(x) - 1)
            ^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: negative dimensions are not allowed

[Azaya89]

I think this is a duplicate of #1414 and can be closed in favour of that one. What do you think @maximlt ?