feat(altair): implement bar-basic

[github-actions]

Implementation: bar-basic - altair

Implements the altair version of bar-basic.

File: plots/bar-basic/implementations/altair.py

Parent Issue: #612

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🤖 impl-generate workflow

[claude]

AI Review - Attempt 1/3

Quality Score: 92/100

Criteria Checklist

Visual Quality

• VQ-001: Axes labeled correctly - "Product Category" (X) and "Sales ($)" (Y)
• VQ-002: Visual clarity - Grid at 0.3 opacity, subtle and doesn't dominate
• VQ-003: Elements clear - Bars clearly visible with good blue color (#306998)
• VQ-004: No overlap - X-axis labels angled at -45°, all readable
• [N/A] VQ-005: Legend - Not needed (single series without color mapping)
• VQ-006: Colorblind safe - Single blue color, no accessibility issues
• VQ-007: Image size - 1600×900 with scale_factor=3.0 = 4800×2700px ✓
• VQ-008: Title - "Product Sales by Category" centered and clear

Code Quality (KISS style for plots - simplified requirements)

• CQ-005: No unexplained magic numbers - Values are clear from context

Correctness

• CR-001: Data accurate - Correct columns (category, value) with realistic data
• CR-002: Spec compliance - All requirements implemented:
  • ✓ Vertical bar chart
  • ✓ Categorical data on x-axis
  • ✓ Heights proportional to values
  • ✓ Consistent bar widths
  • ✓ Good spacing between bars
  • ✓ Single color for all bars
• [N/A] CR-003: Edge cases - N/A for KISS-style plot implementations

Issues Found

None - the implementation meets all quality criteria.

Strengths

1. Excellent Altair idioms: Uses proper encoding types (:N for nominal, :Q for quantitative)
2. Smart sorting: Bars sorted descending by value (sort="-y") for better visual impact
3. Interactive features: Tooltips with proper formatting ($,.0f)
4. Polish details: Subtle rounded corners on bars, clean view with strokeWidth=0
5. Dual output: Both PNG and HTML saved as per library requirements
6. Readable labels: Angled x-axis labels with appropriate font sizes

AI Feedback

This is a well-crafted Altair implementation that follows both the specification and library best practices. The code is clean, idiomatic, and produces a visually appealing chart. The descending sort order is a nice UX touch that wasn't explicitly required but improves readability.

Verdict: APPROVED