update(gantt-dependencies): plotly — Fix misplaced dependency connection lines and ensure correct temporal scheduling

MarkusNeusinger · MarkusNeusinger · commit 39629f68ea43 · 2026-02-25T15:48:05.000+01:00
diff --git a/plots/gantt-dependencies/implementations/plotly.py b/plots/gantt-dependencies/implementations/plotly.py
@@ -1,7 +1,7 @@
-""" pyplots.ai
+"""pyplots.ai
 gantt-dependencies: Gantt Chart with Dependencies
-Library: plotly 6.5.2 | Python 3.13.11
-Quality: 91/100 | Created: 2026-01-15
+Library: plotly 6.5.2 | Python 3.14
+Quality: /100 | Updated: 2026-02-25
 """
 
 import pandas as pd
@@ -42,8 +42,8 @@
     },
     {
         "task": "Database Design",
-        "start": "2024-03-18",
-        "end": "2024-03-24",
+        "start": "2024-03-20",
+        "end": "2024-03-26",
         "group": "Design",
         "depends_on": ["System Architecture"],
     },
@@ -71,8 +71,8 @@
     },
     {
         "task": "Frontend Development",
-        "start": "2024-04-01",
-        "end": "2024-04-18",
+        "start": "2024-03-30",
+        "end": "2024-04-16",
         "group": "Development",
         "depends_on": ["Design Review"],
     },
@@ -85,7 +85,7 @@
     },
     {
         "task": "Integration",
-        "start": "2024-04-15",
+        "start": "2024-04-16",
         "end": "2024-04-22",
         "group": "Development",
         "depends_on": ["Backend API Development", "Frontend Development", "Database Implementation"],
@@ -162,47 +162,47 @@
 
 # Build task list with groups (groups first, then their tasks)
 ordered_tasks = []
-task_to_idx = {}
-idx = 0
+task_y_labels = {}
 
 for group_name in group_order:
     # Add group summary bar
-    ordered_tasks.append({"name": f"▼ {group_name}", "is_group": True, "group": group_name})
-    task_to_idx[f"GROUP_{group_name}"] = idx
-    idx += 1
+    label = f"\u25bc {group_name}"
+    ordered_tasks.append({"name": label, "is_group": True, "group": group_name})
     # Add tasks in this group
     group_tasks = df[df["group"] == group_name].sort_values("start")
     for _, task in group_tasks.iterrows():
-        ordered_tasks.append({"name": f"   {task['task']}", "is_group": False, "task_data": task})
-        task_to_idx[task["task"]] = idx
-        idx += 1
+        label = f"   {task['task']}"
+        ordered_tasks.append({"name": label, "is_group": False, "task_data": task})
+        task_y_labels[task["task"]] = label
 
-# Build y-axis category order
+# Build y-axis category order (reversed so first task appears at top)
 y_categories = [item["name"] for item in ordered_tasks]
 
 # Create figure
 fig = go.Figure()
 
-# Add task bars using timeline-style scatter plot for proper horizontal bars
-for i, item in enumerate(ordered_tasks):
+# Add task bars
+for item in ordered_tasks:
     if item["is_group"]:
-        # Group summary bar
         group_name = item["group"]
         group_data = groups[groups["group"] == group_name].iloc[0]
         fig.add_trace(
             go.Scatter(
                 x=[group_data["start"], group_data["end"]],
                 y=[item["name"], item["name"]],
                 mode="lines",
-                line=dict(color=group_colors[group_name], width=20),
+                line={"color": group_colors[group_name], "width": 20},
                 name=group_name,
                 showlegend=True,
                 legendgroup=group_name,
-                hovertemplate=f"<b>{group_name}</b><br>Start: {group_data['start'].strftime('%Y-%m-%d')}<br>End: {group_data['end'].strftime('%Y-%m-%d')}<extra></extra>",
+                hovertemplate=(
+                    f"<b>{group_name}</b><br>"
+                    f"Start: {group_data['start'].strftime('%Y-%m-%d')}<br>"
+                    f"End: {group_data['end'].strftime('%Y-%m-%d')}<extra></extra>"
+                ),
             )
         )
     else:
-        # Individual task bar
         task = item["task_data"]
         group_name = task["group"]
         duration = (task["end"] - task["start"]).days
@@ -211,98 +211,104 @@
                 x=[task["start"], task["end"]],
                 y=[item["name"], item["name"]],
                 mode="lines",
-                line=dict(color=group_colors[group_name], width=14),
+                line={"color": group_colors[group_name], "width": 14},
                 opacity=0.85,
                 showlegend=False,
                 legendgroup=group_name,
-                hovertemplate=f"<b>{task['task']}</b><br>Start: {task['start'].strftime('%Y-%m-%d')}<br>End: {task['end'].strftime('%Y-%m-%d')}<br>Duration: {duration} days<extra></extra>",
+                hovertemplate=(
+                    f"<b>{task['task']}</b><br>"
+                    f"Start: {task['start'].strftime('%Y-%m-%d')}<br>"
+                    f"End: {task['end'].strftime('%Y-%m-%d')}<br>"
+                    f"Duration: {duration} days<extra></extra>"
+                ),
             )
         )
 
-# Add dependency arrows using shapes for better control
-shapes = []
+# Add dependency arrows as annotations with arrowheads
 for item in ordered_tasks:
     if not item["is_group"]:
         task = item["task_data"]
-        task_name = task["task"]
         depends_on = task["depends_on"]
         if depends_on:
             for dep in depends_on:
-                if dep in task_to_idx:
-                    # Find predecessor task data
+                if dep in task_y_labels:
                     pred_task = df[df["task"] == dep].iloc[0]
                     pred_end = pred_task["end"]
                     curr_start = task["start"]
-                    pred_idx = task_to_idx[dep]
-                    curr_idx = task_to_idx[task_name]
+                    pred_y = task_y_labels[dep]
+                    curr_y = task_y_labels[task["task"]]
 
-                    # Draw line from end of predecessor to start of current task
-                    # Using shapes for connector lines
-                    shapes.append(
-                        dict(
-                            type="line",
-                            x0=pred_end,
-                            y0=pred_idx,
-                            x1=curr_start,
-                            y1=curr_idx,
-                            xref="x",
-                            yref="y",
-                            line=dict(color="#555555", width=1.5, dash="dot"),
-                            opacity=0.5,
-                        )
+                    # Annotation arrow from predecessor end to successor start
+                    fig.add_annotation(
+                        x=curr_start,
+                        y=curr_y,
+                        ax=pred_end,
+                        ay=pred_y,
+                        xref="x",
+                        yref="y",
+                        axref="x",
+                        ayref="y",
+                        showarrow=True,
+                        arrowhead=3,
+                        arrowsize=1.2,
+                        arrowwidth=1.5,
+                        arrowcolor="#555555",
+                        opacity=0.7,
                     )
 
-# Update layout
+# Layout
 fig.update_layout(
-    title=dict(
-        text="gantt-dependencies · plotly · pyplots.ai", font=dict(size=32, color="#333333"), x=0.5, xanchor="center"
-    ),
-    xaxis=dict(
-        title=dict(text="Timeline (2024)", font=dict(size=24)),
-        tickfont=dict(size=14),
-        type="date",
-        tickformat="%b %d",
-        gridcolor="rgba(0,0,0,0.08)",
-        showgrid=True,
-        dtick=7 * 24 * 60 * 60 * 1000,  # Weekly ticks (in milliseconds)
-        tickangle=45,
-    ),
-    yaxis=dict(
-        title=dict(text="", font=dict(size=22)),
-        tickfont=dict(size=15),
-        categoryorder="array",
-        categoryarray=y_categories[::-1],
-        showgrid=False,
-    ),
+    title={
+        "text": "gantt-dependencies \u00b7 plotly \u00b7 pyplots.ai",
+        "font": {"size": 32, "color": "#333333"},
+        "x": 0.5,
+        "xanchor": "center",
+    },
+    xaxis={
+        "title": {"text": "Timeline (2024)", "font": {"size": 24}},
+        "tickfont": {"size": 16},
+        "type": "date",
+        "tickformat": "%b %d",
+        "gridcolor": "rgba(0,0,0,0.08)",
+        "showgrid": True,
+        "dtick": 7 * 24 * 60 * 60 * 1000,
+        "tickangle": 45,
+    },
+    yaxis={
+        "title": {"text": "", "font": {"size": 22}},
+        "tickfont": {"size": 15},
+        "categoryorder": "array",
+        "categoryarray": y_categories[::-1],
+        "showgrid": False,
+    },
     template="plotly_white",
-    shapes=shapes,
-    legend=dict(
-        title=dict(text="Project Phases", font=dict(size=20)),
-        font=dict(size=16),
-        orientation="h",
-        yanchor="bottom",
-        y=1.02,
-        xanchor="center",
-        x=0.5,
-        itemwidth=30,
-    ),
-    margin=dict(l=220, r=60, t=130, b=100),
+    legend={
+        "title": {"text": "Project Phases", "font": {"size": 20}},
+        "font": {"size": 16},
+        "orientation": "h",
+        "yanchor": "bottom",
+        "y": 1.02,
+        "xanchor": "center",
+        "x": 0.5,
+        "itemwidth": 30,
+    },
+    margin={"l": 230, "r": 40, "t": 120, "b": 90},
     height=900,
     width=1600,
 )
 
-# Add annotation for dependency legend
+# Dependency legend annotation
 fig.add_annotation(
     x=1.0,
     y=-0.1,
     xref="paper",
     yref="paper",
-    text="····· Dependency (finish-to-start)",
+    text="\u2192 Dependency (finish-to-start)",
     showarrow=False,
-    font=dict(size=15, color="#555555"),
+    font={"size": 15, "color": "#555555"},
     xanchor="right",
 )
 
-# Save outputs
+# Save
 fig.write_image("plot.png", width=1600, height=900, scale=3)
 fig.write_html("plot.html")
diff --git a/plots/gantt-dependencies/metadata/plotly.yaml b/plots/gantt-dependencies/metadata/plotly.yaml
@@ -1,16 +1,16 @@
 library: plotly
 specification_id: gantt-dependencies
 created: '2026-01-15T21:03:27Z'
-updated: '2026-01-15T21:06:15Z'
-generated_by: claude-opus-4-5-20251101
+updated: '2026-02-25T14:40:00Z'
+generated_by: claude-opus-4-6
 workflow_run: 21046151828
 issue: 3830
-python_version: 3.13.11
+python_version: '3.14'
 library_version: 6.5.2
 preview_url: https://storage.googleapis.com/pyplots-images/plots/gantt-dependencies/plotly/plot.png
 preview_thumb: https://storage.googleapis.com/pyplots-images/plots/gantt-dependencies/plotly/plot_thumb.png
 preview_html: https://storage.googleapis.com/pyplots-images/plots/gantt-dependencies/plotly/plot.html
-quality_score: 91
+quality_score: null
 review:
   strengths:
   - Excellent hierarchical organization with group summary bars and indented child
diff --git a/plots/gantt-dependencies/specification.md b/plots/gantt-dependencies/specification.md
@@ -23,10 +23,11 @@ A Gantt chart that visualizes project schedules with task dependencies and group
 
 ## Notes
 
-- Draw dependency arrows/connectors from the end of predecessor tasks to the start of successor tasks
+- Draw dependency arrows from the right edge (end date) of each predecessor bar to the left edge (start date) of the successor bar
 - Use different visual styles for dependency types (finish-to-start is most common)
 - Group headers should show aggregate timeline spanning from earliest to latest task in the group
 - Consider indentation or color coding to distinguish groups from individual tasks
 - Arrows should avoid overlapping task bars where possible
 - Include a legend explaining dependency line styles if multiple types are used
+- Dependent tasks must be scheduled to start at or after the end of their predecessor — never before
 - Vertical alignment should clearly show task hierarchy (groups above their child tasks)
diff --git a/plots/gantt-dependencies/specification.yaml b/plots/gantt-dependencies/specification.yaml
@@ -6,7 +6,7 @@ title: Gantt Chart with Dependencies
 
 # Specification tracking
 created: 2026-01-15T20:43:22Z
-updated: 2026-01-15T20:43:22Z
+updated: 2026-02-25T12:00:00Z
 issue: 3830
 suggested: Eifi1
 
@@ -27,3 +27,5 @@ tags:
     - grouped
     - hierarchical
     - annotated
+    - temporal
+    - dependencies
