feat(letsplot): implement point-and-figure-basic (#3864)

## Implementation: `point-and-figure-basic` - letsplot

Implements the **letsplot** version of `point-and-figure-basic`.

**File:** `plots/point-and-figure-basic/implementations/letsplot.py`

**Parent Issue:** #3755

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/21047207459)*

---------

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/point-and-figure-basic/implementations/letsplot.py

@@ -0,0 +1,123 @@
+""" pyplots.ai
+point-and-figure-basic: Point and Figure Chart
+Library: letsplot 4.8.2 | Python 3.13.11
+Quality: 91/100 | Created: 2026-01-15
+"""
+
+import numpy as np
+import pandas as pd
+from lets_plot import (
+    LetsPlot,
+    aes,
+    element_blank,
+    element_text,
+    geom_text,
+    ggplot,
+    ggsize,
+    labs,
+    scale_color_manual,
+    scale_x_continuous,
+    scale_y_continuous,
+    theme,
+    theme_minimal,
+)
+from lets_plot.export import ggsave
+
+
+LetsPlot.setup_html()
+
+# Generate synthetic stock price data
+np.random.seed(42)
+n_days = 300
+
+# Create realistic price movement with trends
+returns = np.random.normal(0.001, 0.02, n_days)
+returns[50:100] += 0.005  # Uptrend
+returns[150:200] -= 0.004  # Downtrend
+returns[250:280] += 0.006  # Uptrend
+
+prices = 100 * np.cumprod(1 + returns)
+
+# Point and Figure parameters
+box_size = 2.0  # Each box represents $2
+reversal = 3  # 3-box reversal
+
+# Build Point and Figure chart data (inline)
+pnf_rows = []  # List of (column_index, price_level, symbol, direction)
+current_box = int(prices[0] / box_size) * box_size
+direction = None
+column_idx = 0
+
+for price in prices:
+    price_box = int(price / box_size) * box_size
+
+    if direction is None:
+        # First move determines direction
+        if price_box > current_box:
+            direction = "up"
+            for b in range(int(current_box / box_size), int(price_box / box_size) + 1):
+                pnf_rows.append((column_idx, b * box_size, "X", "up"))
+            current_box = price_box
+        elif price_box < current_box:
+            direction = "down"
+            for b in range(int(price_box / box_size), int(current_box / box_size) + 1):
+                pnf_rows.append((column_idx, b * box_size, "O", "down"))
+            current_box = price_box
+
+    elif direction == "up":
+        if price_box > current_box:
+            # Continue up
+            for b in range(int(current_box / box_size) + 1, int(price_box / box_size) + 1):
+                pnf_rows.append((column_idx, b * box_size, "X", "up"))
+            current_box = price_box
+        elif price_box <= current_box - reversal * box_size:
+            # Reversal down
+            column_idx += 1
+            for b in range(int(price_box / box_size), int(current_box / box_size)):
+                pnf_rows.append((column_idx, b * box_size, "O", "down"))
+            current_box = price_box
+            direction = "down"
+
+    elif direction == "down":
+        if price_box < current_box:
+            # Continue down
+            for b in range(int(price_box / box_size), int(current_box / box_size)):
+                pnf_rows.append((column_idx, b * box_size, "O", "down"))
+            current_box = price_box
+        elif price_box >= current_box + reversal * box_size:
+            # Reversal up
+            column_idx += 1
+            for b in range(int(current_box / box_size) + 1, int(price_box / box_size) + 1):
+                pnf_rows.append((column_idx, b * box_size, "X", "up"))
+            current_box = price_box
+            direction = "up"
+
+# Convert to DataFrame for plotting
+df_pnf = pd.DataFrame(pnf_rows, columns=["column", "price", "symbol", "direction"])
+df_pnf = df_pnf.drop_duplicates(subset=["column", "price"])
+
+# Create the plot using geom_text to display X and O symbols
+plot = (
+    ggplot(df_pnf, aes(x="column", y="price", label="symbol", color="direction"))
+    + geom_text(size=16, fontface="bold")
+    + scale_color_manual(values={"up": "#16a34a", "down": "#dc2626"})
+    + scale_x_continuous(name="Column (Reversal Number)")
+    + scale_y_continuous(name="Price ($)")
+    + labs(title="point-and-figure-basic · letsplot · pyplots.ai")
+    + theme_minimal()
+    + theme(
+        plot_title=element_text(size=24, face="bold"),
+        axis_title=element_text(size=20),
+        axis_text=element_text(size=16),
+        legend_position="none",
+        panel_grid_major_x=element_blank(),
+        panel_grid_minor_x=element_blank(),
+    )
+    + ggsize(1600, 900)
+)
+
+# Save PNG (scale 3x for 4800 × 2700 px)
+ggsave(plot, "plot.png", path=".", scale=3)
+
+# Save HTML for interactivity
+ggsave(plot, "plot.html", path=".")

plots/point-and-figure-basic/metadata/letsplot.yaml

@@ -0,0 +1,212 @@
+library: letsplot
+specification_id: point-and-figure-basic
+created: '2026-01-15T21:43:30Z'
+updated: '2026-01-15T21:47:33Z'
+generated_by: claude-opus-4-5-20251101
+workflow_run: 21047207459
+issue: 3755
+python_version: 3.13.11
+library_version: 4.8.2
+preview_url: https://storage.googleapis.com/pyplots-images/plots/point-and-figure-basic/letsplot/plot.png
+preview_thumb: https://storage.googleapis.com/pyplots-images/plots/point-and-figure-basic/letsplot/plot_thumb.png
+preview_html: https://storage.googleapis.com/pyplots-images/plots/point-and-figure-basic/letsplot/plot.html
+quality_score: 91
+review:
+  strengths:
+  - Excellent implementation of the P&F algorithm with correct box size and 3-box
+    reversal logic
+  - Clean use of lets-plot ggplot2-style grammar with appropriate aesthetics mapping
+  - Perfect title format and axis labeling with descriptive names and units
+  - Good color choices with green/red that also include shape distinction (X/O) for
+    accessibility
+  - Proper handling of column-based (not time-based) X-axis which is key to P&F charts
+  - High-resolution export with scale=3 for 4800x2700 output
+  weaknesses:
+  - Grid styling could be improved - horizontal grid is visible but could use more
+    subtle alpha
+  - The X and O symbols could be slightly larger/bolder for better visual impact at
+    the target resolution
+  - Spec mentions adding support/resistance trend lines which are not implemented
+    (optional per spec)
+  image_description: The plot displays a Point and Figure (P&F) chart with green X
+    symbols representing rising price columns (bullish) and red O symbols representing
+    falling price columns (bearish). The chart shows price movement from approximately
+    $80 to $155 across 23 columns (reversal numbers 0-22). The X-axis is labeled "Column
+    (Reversal Number)" and Y-axis is labeled "Price ($)". The title correctly displays
+    "point-and-figure-basic · letsplot · pyplots.ai". The chart demonstrates clear
+    alternating columns of X's and O's with appropriate spacing, showing multiple
+    trends including uptrends and downtrends. The overall layout is clean with a minimal
+    theme, subtle horizontal grid lines, and no legend (appropriately hidden since
+    color coding is self-explanatory).
+  criteria_checklist:
+    visual_quality:
+      score: 36
+      max: 40
+      items:
+      - id: VQ-01
+        name: Text Legibility
+        score: 10
+        max: 10
+        passed: true
+        comment: Title, axis labels, and tick marks are all clearly readable at full
+          size
+      - id: VQ-02
+        name: No Overlap
+        score: 8
+        max: 8
+        passed: true
+        comment: No overlapping text or symbols
+      - id: VQ-03
+        name: Element Visibility
+        score: 6
+        max: 8
+        passed: true
+        comment: X and O symbols are visible and appropriately sized, though could
+          be slightly bolder
+      - id: VQ-04
+        name: Color Accessibility
+        score: 5
+        max: 5
+        passed: true
+        comment: Green and red are distinguishable, X vs O shape provides secondary
+          distinction
+      - id: VQ-05
+        name: Layout Balance
+        score: 5
+        max: 5
+        passed: true
+        comment: Good use of canvas space, plot fills majority of area with balanced
+          margins
+      - id: VQ-06
+        name: Axis Labels
+        score: 2
+        max: 2
+        passed: true
+        comment: Price ($) and Column (Reversal Number) are descriptive with units
+      - id: VQ-07
+        name: Grid & Legend
+        score: 0
+        max: 2
+        passed: false
+        comment: Legend hidden appropriately but horizontal grid could be more subtle
+    spec_compliance:
+      score: 25
+      max: 25
+      items:
+      - id: SC-01
+        name: Plot Type
+        score: 8
+        max: 8
+        passed: true
+        comment: Correct Point and Figure chart with X and O columns
+      - id: SC-02
+        name: Data Mapping
+        score: 5
+        max: 5
+        passed: true
+        comment: Columns represent reversals, Y-axis shows price levels
+      - id: SC-03
+        name: Required Features
+        score: 5
+        max: 5
+        passed: true
+        comment: Uses X for rising, O for falling, green for bullish, red for bearish,
+          3-box reversal
+      - id: SC-04
+        name: Data Range
+        score: 3
+        max: 3
+        passed: true
+        comment: Full price range visible from ~$80 to ~$155
+      - id: SC-05
+        name: Legend Accuracy
+        score: 2
+        max: 2
+        passed: true
+        comment: No legend needed, color/symbol mapping is standard P&F convention
+      - id: SC-06
+        name: Title Format
+        score: 2
+        max: 2
+        passed: true
+        comment: Correctly formatted as point-and-figure-basic · letsplot · pyplots.ai
+    data_quality:
+      score: 18
+      max: 20
+      items:
+      - id: DQ-01
+        name: Feature Coverage
+        score: 7
+        max: 8
+        passed: true
+        comment: Shows both uptrends and downtrends, multiple reversals, but could
+          show more distinct support/resistance patterns
+      - id: DQ-02
+        name: Realistic Context
+        score: 7
+        max: 7
+        passed: true
+        comment: Stock price simulation with realistic price movements and trends
+      - id: DQ-03
+        name: Appropriate Scale
+        score: 4
+        max: 5
+        passed: true
+        comment: Price range $80-155 is realistic for stocks, box size of $2 is appropriate
+    code_quality:
+      score: 9
+      max: 10
+      items:
+      - id: CQ-01
+        name: KISS Structure
+        score: 3
+        max: 3
+        passed: true
+        comment: 'Linear flow: imports → data generation → P&F algorithm → plot →
+          save'
+      - id: CQ-02
+        name: Reproducibility
+        score: 3
+        max: 3
+        passed: true
+        comment: Uses np.random.seed(42)
+      - id: CQ-03
+        name: Clean Imports
+        score: 2
+        max: 2
+        passed: true
+        comment: All imports are used
+      - id: CQ-04
+        name: No Deprecated API
+        score: 1
+        max: 1
+        passed: true
+        comment: Uses current lets-plot API
+      - id: CQ-05
+        name: Output Correct
+        score: 0
+        max: 1
+        passed: false
+        comment: Saves to plot.png but path argument is explicit rather than implicit
+    library_features:
+      score: 3
+      max: 5
+      items:
+      - id: LF-01
+        name: Distinctive Features
+        score: 3
+        max: 5
+        passed: true
+        comment: Uses geom_text for symbol rendering, ggplot grammar, theme customization,
+          and ggsave with scale parameter
+  verdict: APPROVED
+impl_tags:
+  dependencies: []
+  techniques:
+  - html-export
+  patterns:
+  - data-generation
+  - iteration-over-groups
+  dataprep: []
+  styling:
+  - grid-styling