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fix: continuous colorscale strings with discrete-only chart types #46

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Merged
FBumann merged 1 commit into from
Mar 9, 2026
Merged

fix: continuous colorscale strings with discrete-only chart types #46

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30 changes: 28 additions & 2 deletions xarray_plotly/common.py
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@

if TYPE_CHECKING:
import pandas as pd
from xarray import DataArray
from xarray import DataArray, Dataset


class _AUTO:
Expand Down Expand Up @@ -251,7 +251,21 @@ def _get_qualitative_scale_names() -> frozenset[str]:
)


def resolve_colors(colors: Colors, px_kwargs: dict[str, Any]) -> dict[str, Any]:
def _sample_colorscale(name: str, n: int) -> list[str]:
"""Sample *n* evenly-spaced colors from a named Plotly colorscale."""
scale = px.colors.get_colorscale(name)
samplepoints = [i / max(n - 1, 1) for i in range(n)]
result: list[str] = px.colors.sample_colorscale(scale, samplepoints)
return result


def resolve_colors(
colors: Colors,
px_kwargs: dict[str, Any],
*,
color_dim: Hashable | None = None,
darray: DataArray | Dataset | None = None,
) -> dict[str, Any]:
"""Map unified `colors` parameter to appropriate Plotly px_kwargs.

Direct color_* kwargs take precedence and trigger a warning if
Expand All @@ -260,6 +274,14 @@ def resolve_colors(colors: Colors, px_kwargs: dict[str, Any]) -> dict[str, Any]:
Args:
colors: Unified color specification (str, list, dict, or None).
px_kwargs: Existing kwargs to pass to Plotly Express.
color_dim: Dimension name used for discrete color grouping.
When provided together with *darray*, a continuous colorscale
string is sampled into a discrete sequence whose length
matches the number of coordinates along this dimension.
Use for chart types that only accept discrete color
parameters (line, area, box, pie).
darray: Source DataArray or Dataset; used with *color_dim* to
determine the number of discrete colors to sample.

Returns:
Updated px_kwargs with color parameters injected.
Expand All @@ -284,6 +306,10 @@ def resolve_colors(colors: Colors, px_kwargs: dict[str, Any]) -> dict[str, Any]:
# Check if it's a qualitative (discrete) palette name
if colors in _get_qualitative_scale_names():
px_kwargs["color_discrete_sequence"] = getattr(px.colors.qualitative, colors)
elif color_dim is not None and darray is not None:
# Sample from continuous scale into a discrete sequence
n = darray.sizes[color_dim]
px_kwargs["color_discrete_sequence"] = _sample_colorscale(colors, n)
else:
# Assume continuous scale
px_kwargs["color_continuous_scale"] = colors
Expand Down
10 changes: 5 additions & 5 deletions xarray_plotly/plotting.py
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Original file line number Diff line number Diff line change
Expand Up @@ -82,7 +82,6 @@ def line(
-------
plotly.graph_objects.Figure
"""
px_kwargs = resolve_colors(colors, px_kwargs)
slots = assign_slots(
list(darray.dims),
"line",
Expand All @@ -94,6 +93,7 @@ def line(
facet_row=facet_row,
animation_frame=animation_frame,
)
px_kwargs = resolve_colors(colors, px_kwargs, color_dim=slots.get("color"), darray=darray)

df = to_dataframe(darray)
value_col = get_value_col(darray)
Expand Down Expand Up @@ -329,7 +329,6 @@ def fast_bar(
-------
plotly.graph_objects.Figure
"""
px_kwargs = resolve_colors(colors, px_kwargs)
slots = assign_slots(
list(darray.dims),
"fast_bar",
Expand All @@ -339,6 +338,7 @@ def fast_bar(
facet_row=facet_row,
animation_frame=animation_frame,
)
px_kwargs = resolve_colors(colors, px_kwargs, color_dim=slots.get("color"), darray=darray)

df = to_dataframe(darray)
value_col = get_value_col(darray)
Expand Down Expand Up @@ -410,7 +410,6 @@ def area(
-------
plotly.graph_objects.Figure
"""
px_kwargs = resolve_colors(colors, px_kwargs)
slots = assign_slots(
list(darray.dims),
"area",
Expand All @@ -421,6 +420,7 @@ def area(
facet_row=facet_row,
animation_frame=animation_frame,
)
px_kwargs = resolve_colors(colors, px_kwargs, color_dim=slots.get("color"), darray=darray)

df = to_dataframe(darray)
value_col = get_value_col(darray)
Expand Down Expand Up @@ -487,7 +487,6 @@ def box(
-------
plotly.graph_objects.Figure
"""
px_kwargs = resolve_colors(colors, px_kwargs)
slots = assign_slots(
list(darray.dims),
"box",
Expand All @@ -498,6 +497,7 @@ def box(
facet_row=facet_row,
animation_frame=animation_frame,
)
px_kwargs = resolve_colors(colors, px_kwargs, color_dim=slots.get("color"), darray=darray)

df = to_dataframe(darray)
value_col = get_value_col(darray)
Expand Down Expand Up @@ -746,14 +746,14 @@ def pie(
-------
plotly.graph_objects.Figure
"""
px_kwargs = resolve_colors(colors, px_kwargs)
slots = assign_slots(
list(darray.dims),
"pie",
names=names,
facet_col=facet_col,
facet_row=facet_row,
)
px_kwargs = resolve_colors(colors, px_kwargs, color_dim=slots.get("names"), darray=darray)

df = to_dataframe(darray)
value_col = get_value_col(darray)
Expand Down