feat: add fast_bar() method for high-performance bar-like charts

[FBumann]

Summary

Adds fast_bar() method that creates bar-like visualizations using stacked areas. Renders significantly faster than bar() for large datasets because it uses a single polygon per trace instead of individual rectangles.

Features

• Stepped area rendering - Uses px.area with line_shape='hv' and no outline for bar-like appearance

• Smart sign handling - Classifies traces and assigns appropriate stackgroups:

  Trace values	Stackgroup	Visual
  All positive	'positive'	Solid fill, stacks upward
  All negative	'negative'	Solid fill, stacks downward
  Mixed +/-	None	Dashed line + warning

• Faceting & animation support - Works with facet_col, facet_row, animation_frame

• User warning - Warns when traces have mixed signs and recommends using bar()

API

from xarray_plotly import xpx

# Basic usage
fig = xpx(da).fast_bar()

# With faceting and animation
fig = xpx(da).fast_bar(facet_col="region", animation_frame="year")

# Positive/negative data stacks correctly
da_financials = ...  # Revenue (positive), Costs (negative)
fig = xpx(da_financials).fast_bar()  # Stacks up and down from zero

When to use

Method	Use when...
fast_bar()	Large datasets, animations, performance matters, same-sign per trace
bar()	Need grouped bars, pattern fills, or mixed +/- values per trace

Changes

• plotting.py: Added fast_bar() function and _style_traces_as_bars() helper
• config.py: Added fast_bar slot order
• accessor.py: Added fast_bar() to both DataArrayPlotlyAccessor and DatasetPlotlyAccessor
• test_accessor.py: Added 6 tests for fast_bar behavior
• docs/examples/fast_bar.ipynb: Comprehensive examples with faceting, animation, and sign handling

Test plan

• 107 tests passing
• Faceting support verified
• Animation support verified
• Positive/negative stacking verified
• Mixed sign warning verified

Summary by CodeRabbit

• New Features

  • Introduced fast_bar() visualization method for creating performance-optimized bar charts
  • Supports faceting by columns and animating across dimensions
  • Intelligently handles positive and negative values with appropriate stacking behavior

• Documentation

  • Added comprehensive notebook examples demonstrating fast_bar() usage, including faceting, animation, and best practices

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[coderabbitai]

Caution

Review failed

The pull request is closed.

📝 Walkthrough

Walkthrough

A new fast_bar visualization is added: plotting.fast_bar implements area-based bar rendering with trace sign classification and styling; DataArrayPlotlyAccessor and DatasetPlotlyAccessor gain .fast_bar methods; DEFAULT_SLOT_ORDERS updated; tests and a docs example notebook plus mkdocs nav entries were added.

Changes

Cohort / File(s)	Summary
Documentation & Examples docs/examples/fast_bar.ipynb, mkdocs.yml	New example notebook demonstrating fast_bar usage (basic, faceting, animation, mixed-sign behavior) and added mkdocs navigation entries for examples.
Plotting implementation xarray_plotly/plotting.py	Added public fast_bar() plus helpers _classify_trace_sign() and _style_traces_as_bars(); uses plotly.express.area then post-processes traces for sign-aware stacking and dashed rendering for mixed-sign traces; emits warnings for mixed traces.
Accessors xarray_plotly/accessor.py	Added fast_bar methods to DataArrayPlotlyAccessor and DatasetPlotlyAccessor (Dataset version accepts var), and exported them via __all__.
Configuration xarray_plotly/config.py	Added DEFAULT_SLOT_ORDERS entry for "fast_bar": ("x","color","facet_col","facet_row","animation_frame").
Tests tests/test_accessor.py	New tests verifying fast_bar returns a Figure, trace styling (line width/shape/fill), animation-frame handling, dashed styling for mixed-sign traces, stackgroup separation by sign, and stacking for same-sign traces.

Sequence Diagram

sequenceDiagram
    participant User
    participant Accessor as DataArrayPlotly<br/>Accessor
    participant Plotting as plotting<br/>module
    participant Express as plotly.express
    participant Figure as go.Figure

    User->>Accessor: .fast_bar(x, color, facet_col, animation_frame)
    Accessor->>Plotting: fast_bar(darray, x=..., color=..., ...)
    Plotting->>Express: area(..., x=..., color=..., facet_col=..., animation_frame=...)
    Express-->>Plotting: Figure with area traces
    Plotting->>Plotting: _style_traces_as_bars(fig)
    rect rgba(100,150,200,0.5)
        Note over Plotting: classify trace signs, assign stackgroups,\napply fill/stroke/dash styling, warn on mixed-signs
    end
    Plotting-->>Accessor: styled go.Figure
    Accessor-->>User: go.Figure

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Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• Add dataset plotting accessor #2: Related changes to accessor implementations and dataset accessor patterns; touches the same accessor classes extended here.

Poem

🐰 I hop, I sketch with speed and cheer,
Fast bars that stack both far and near,
Positives rise, negatives fall,
Mixed signs dash — I warn them all!
A nimble chart to celebrate here. 🎨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Title check	✅ Passed	The title accurately summarizes the main change: adding a new fast_bar() method for high-performance bar-like charts, which is the primary feature introduced across accessor, plotting, config, documentation, and test files.

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✨ Finishing touches

• 📝 Generate docstrings

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Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@xarray_plotly/accessor.py`:
- Around line 163-196: The fast_bar accessor method is not exported via __all__,
so it won't show up in tab-completion; update the module-level __all__ to
include "fast_bar" (and add it to the __all__ list for both accessor exports if
there are two accessor modules/objects) so that __dir__ can discover it; locate
the fast_bar definition in accessor.py and ensure the string "fast_bar" is
present in the module's __all__ sequence alongside the other accessor names.

🧹 Nitpick comments (1)

xarray_plotly/plotting.py (1)

171-185: Consider reusing _classify_trace_sign to avoid duplicate logic.
Right now classification is re-implemented in _style_traces_as_bars; either use the helper or remove it to keep one source of truth.