feat(matplotlib): implement marimekko-basic (#1087)

## Implementation: `marimekko-basic` - matplotlib

Implements the **matplotlib** version of `marimekko-basic`.

**File:** `plots/marimekko-basic/implementations/matplotlib.py`

**Parent Issue:** #1002

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/20280360884)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/marimekko-basic/implementations/matplotlib.py

@@ -0,0 +1,114 @@
+"""
+marimekko-basic: Basic Marimekko Chart
+Library: matplotlib
+"""
+
+import matplotlib.pyplot as plt
+import numpy as np
+
+
+# Data: Market share by region (x-category) and product line (y-category)
+# Regions have different total market sizes (determines bar widths)
+# Products have different shares within each region (determines segment heights)
+regions = ["North America", "Europe", "Asia Pacific", "Latin America"]
+products = ["Electronics", "Apparel", "Home & Garden", "Sports"]
+
+# Values matrix: rows = products, columns = regions
+# Each column total determines that region's bar width
+values = np.array(
+    [
+        [120, 85, 200, 35],  # Electronics
+        [80, 110, 150, 45],  # Apparel
+        [60, 70, 80, 25],  # Home & Garden
+        [40, 35, 70, 15],  # Sports
+    ]
+)
+
+# Colors - Python blue/yellow first, then colorblind-safe additions
+colors = ["#306998", "#FFD43B", "#4DAF4A", "#984EA3"]
+
+# Calculate bar widths (proportional to column totals)
+column_totals = values.sum(axis=0)
+total = column_totals.sum()
+bar_widths = column_totals / total
+
+# Calculate cumulative widths for x-positioning
+cum_widths = np.concatenate([[0], np.cumsum(bar_widths)[:-1]])
+
+# Create figure (4800x2700 px at dpi=300)
+fig, ax = plt.subplots(figsize=(16, 9))
+
+# Draw each segment
+for i, (product, color) in enumerate(zip(products, colors, strict=True)):
+    # Calculate heights as proportion of column total
+    heights = values[i] / column_totals
+
+    # Calculate bottom positions (cumulative heights of products below)
+    bottoms = values[:i].sum(axis=0) / column_totals if i > 0 else np.zeros(len(regions))
+
+    # Draw bars for this product across all regions
+    for j in range(len(regions)):
+        ax.bar(
+            cum_widths[j] + bar_widths[j] / 2,
+            heights[j],
+            width=bar_widths[j] * 0.98,  # Small gap between bars
+            bottom=bottoms[j],
+            color=color,
+            edgecolor="white",
+            linewidth=2,
+            label=product if j == 0 else None,
+        )
+
+        # Add value labels on larger segments
+        if heights[j] > 0.12:
+            ax.text(
+                cum_widths[j] + bar_widths[j] / 2,
+                bottoms[j] + heights[j] / 2,
+                f"${values[i, j]}M",
+                ha="center",
+                va="center",
+                fontsize=14,
+                fontweight="bold",
+                color="white" if color == "#306998" else "black",
+            )
+
+# Add region labels at the bottom
+for j, region in enumerate(regions):
+    ax.text(
+        cum_widths[j] + bar_widths[j] / 2,
+        -0.05,
+        f"{region}\n(${column_totals[j]:.0f}M)",
+        ha="center",
+        va="top",
+        fontsize=16,
+        fontweight="bold",
+    )
+
+# Style the plot
+ax.set_xlim(0, 1)
+ax.set_ylim(-0.15, 1)
+ax.set_ylabel("Share within Region", fontsize=20)
+ax.set_title("marimekko-basic · matplotlib · pyplots.ai", fontsize=24)
+
+# Format y-axis as percentage
+ax.set_yticks([0, 0.25, 0.5, 0.75, 1.0])
+ax.set_yticklabels(["0%", "25%", "50%", "75%", "100%"])
+ax.tick_params(axis="y", labelsize=16)
+
+# Remove x-axis ticks (we have custom labels)
+ax.set_xticks([])
+
+# Add legend
+ax.legend(loc="upper left", bbox_to_anchor=(1.02, 1), fontsize=16, title="Product Lines", title_fontsize=18)
+
+# Subtle grid on y-axis only
+ax.yaxis.grid(True, alpha=0.3, linestyle="--")
+ax.set_axisbelow(True)
+
+# Remove top and right spines
+ax.spines["top"].set_visible(False)
+ax.spines["right"].set_visible(False)
+ax.spines["bottom"].set_visible(False)
+
+plt.tight_layout()
+plt.savefig("plot.png", dpi=300, bbox_inches="tight")

plots/marimekko-basic/metadata/matplotlib.yaml

@@ -0,0 +1,23 @@
+# Per-library metadata for matplotlib implementation of marimekko-basic
+# Auto-generated by impl-generate.yml
+
+library: matplotlib
+specification_id: marimekko-basic
+
+# Preview URLs (filled by workflow)
+preview_url: https://storage.googleapis.com/pyplots-images/plots/marimekko-basic/matplotlib/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/marimekko-basic/matplotlib/plot_thumb.png
+preview_html: null
+
+current:
+  version: 0
+  generated_at: 2025-12-16T19:40:17Z
+  generated_by: claude-opus-4-5-20251101
+  workflow_run: 20280360884
+  issue: 1002
+  quality_score: 94
+  # Version info (filled by workflow)
+  python_version: "3.13.11"
+  library_version: "unknown"
+
+history: []