data-analysis

Data Analysis Skill

Overview

This skill analyzes user-uploaded Excel/CSV files using DuckDB — an in-process analytical SQL engine. It supports schema inspection, SQL-based querying, statistical summaries, and result export, all through a single Python script.

Environment setup

Prepare the Python environment before running analyses. Install the required packages explicitly using the same interpreter that will run the script:

python -m pip install duckdb openpyxl

If either package is missing, the script exits with a setup instruction; it does not invoke an installer or modify the environment. DuckDB's existing spatial-extension setup for loading files is unchanged.

Core Capabilities

• Inspect Excel/CSV file structure (sheets, columns, types, row counts)
• Execute arbitrary SQL queries against uploaded data
• Generate statistical summaries (mean, median, stddev, percentiles, nulls)
• Support multi-sheet Excel workbooks (each sheet becomes a table)
• Export query results to CSV, JSON, or Markdown
• Handle large files efficiently with DuckDB's columnar engine

Workflow

Step 1: Understand Requirements

When a user uploads data files and requests analysis, identify:

• File location: Path(s) to uploaded Excel/CSV files under /mnt/user-data/uploads/
• Analysis goal: What insights the user wants (summary, filtering, aggregation, comparison, etc.)
• Output format: How results should be presented (table, CSV export, JSON, etc.)
• You don't need to check the folder under /mnt/user-data

Step 2: Inspect File Structure

First, inspect the uploaded file to understand its schema:

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/data.xlsx \
  --action inspect

This returns:

• Sheet names (for Excel) or filename (for CSV)
• Column names, data types, and non-null counts
• Row count per sheet/file
• Sample data (first 5 rows)

Step 3: Perform Analysis

Based on the schema, construct SQL queries to answer the user's questions.

Run SQL Query

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/data.xlsx \
  --action query \
  --sql "SELECT category, COUNT(*) as count, AVG(amount) as avg_amount FROM Sheet1 GROUP BY category ORDER BY count DESC"

Generate Statistical Summary

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/data.xlsx \
  --action summary \
  --table Sheet1

This returns for each numeric column: count, mean, std, min, 25%, 50%, 75%, max, nullcount. For string columns: count, unique, top value, frequency, nullcount.

Export Results

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/data.xlsx \
  --action query \
  --sql "SELECT * FROM Sheet1 WHERE amount > 1000" \
  --output-file /mnt/user-data/outputs/filtered-results.csv

Supported output formats (auto-detected from extension):

• .csv — Comma-separated values
• .json — JSON array of records
• .md — Markdown table

JSON result column names must be unique. Use explicit SQL aliases for repeated names, for example SELECT a.id AS left_id, b.id AS right_id FROM .... Duplicate names cause an error and leave any existing output file untouched. The error lists the repeated names so you can alias them directly. The CLI prints a short Error: ... message to stderr and exits nonzero for this rejection.

Parameters

[!NOTE] Do NOT read the Python file, just call it with the parameters.

Table Naming Rules

• Excel files: Each sheet becomes a table named after the sheet (e.g., Sheet1, Sales, Revenue)
• CSV files: Table name is the filename without extension (e.g., data.csv → data)
• Multiple files: All tables from all files are available in the same query context, enabling cross-file joins
• Collisions: Repeated names (including case-only differences) receive unique SQL names in input order, such as report, report_1, report_2. This also applies to repeated Excel sheet names. Use the SQL names shown by inspect for queries and summaries. An original-name alias never overrides an earlier SQL name.
• Special characters: Sheet/file names are sanitized into SQL names (for example, sales-2026 → sales_2026). Use the SQL names printed by inspect, or double-quote a unique original name, e.g., SELECT * FROM "sales-2026". Queries execute unchanged: string literals, column aliases, comments, and CTEs retain normal DuckDB semantics. Names containing a double quote escape it by doubling it, e.g., "net""amount"

Analysis Patterns

Basic Exploration

-- Row count
SELECT COUNT(*) FROM Sheet1

-- Distinct values in a column
SELECT DISTINCT category FROM Sheet1

-- Value distribution
SELECT category, COUNT(*) as cnt FROM Sheet1 GROUP BY category ORDER BY cnt DESC

-- Date range
SELECT MIN(date_col), MAX(date_col) FROM Sheet1

Aggregation & Grouping

-- Revenue by category and month
SELECT category, DATE_TRUNC('month', order_date) as month,
       SUM(revenue) as total_revenue
FROM Sales
GROUP BY category, month
ORDER BY month, total_revenue DESC

-- Top 10 customers by spend
SELECT customer_name, SUM(amount) as total_spend
FROM Orders GROUP BY customer_name
ORDER BY total_spend DESC LIMIT 10

Cross-file Joins

-- Join sales with customer info from different files
SELECT s.order_id, s.amount, c.customer_name, c.region
FROM sales s
JOIN customers c ON s.customer_id = c.id
WHERE s.amount > 500

Window Functions

-- Running total and rank
SELECT order_date, amount,
       SUM(amount) OVER (ORDER BY order_date) as running_total,
       RANK() OVER (ORDER BY amount DESC) as amount_rank
FROM Sales

Pivot-style Analysis

-- Pivot: monthly revenue by category
SELECT category,
       SUM(CASE WHEN MONTH(date) = 1 THEN revenue END) as Jan,
       SUM(CASE WHEN MONTH(date) = 2 THEN revenue END) as Feb,
       SUM(CASE WHEN MONTH(date) = 3 THEN revenue END) as Mar
FROM Sales
GROUP BY category

Complete Example

User uploads sales_2024.xlsx (with sheets: Orders, Products, Customers) and asks: "Analyze my sales data — show top products by revenue and monthly trends."

Step 1: Inspect the file

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/sales_2024.xlsx \
  --action inspect

Step 2: Top products by revenue

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/sales_2024.xlsx \
  --action query \
  --sql "SELECT p.product_name, SUM(o.quantity * o.unit_price) as total_revenue, SUM(o.quantity) as total_units FROM Orders o JOIN Products p ON o.product_id = p.id GROUP BY p.product_name ORDER BY total_revenue DESC LIMIT 10"

Step 3: Monthly revenue trends

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/sales_2024.xlsx \
  --action query \
  --sql "SELECT DATE_TRUNC('month', order_date) as month, SUM(quantity * unit_price) as revenue FROM Orders GROUP BY month ORDER BY month" \
  --output-file /mnt/user-data/outputs/monthly-trends.csv

Step 4: Statistical summary

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/sales_2024.xlsx \
  --action summary \
  --table Orders

Present results to the user with clear explanations of findings, trends, and actionable insights.

Multi-file Example

User uploads orders.csv and customers.xlsx and asks: "Which region has the highest average order value?"

python /mnt/skills/public/data-analysis/scripts/analyze.py \
  --files /mnt/user-data/uploads/orders.csv /mnt/user-data/uploads/customers.xlsx \
  --action query \
  --sql "SELECT c.region, AVG(o.amount) as avg_order_value, COUNT(*) as order_count FROM orders o JOIN Customers c ON o.customer_id = c.id GROUP BY c.region ORDER BY avg_order_value DESC"

Output Handling

After analysis:

• Present query results directly in conversation as formatted tables
• For large results, export to file and share via present_files tool
• Always explain findings in plain language with key takeaways
• Suggest follow-up analyses when patterns are interesting
• Offer to export results if the user wants to keep them

Caching

The script automatically caches loaded data to avoid re-parsing files on every call:

• On first load, files are parsed and stored in a persistent DuckDB database under the system temporary directory (.data-analysis-cache/)
• The cache key hashes the ordered input basenames and a separate SHA256 digest of each file. Renaming, reordering, or changing inputs creates a new cache; moving unchanged, identically named inputs to another directory preserves reuse. The updated key namespace ignores older cached table maps, which are rebuilt on first use
• Subsequent calls with the same files will use the cached database directly (near-instant startup)
• Cache is transparent — no extra parameters needed

This is especially useful when running multiple queries against the same data files (inspect → query → summary).

Notes

• DuckDB supports full SQL including window functions, CTEs, subqueries, and advanced aggregations
• Excel date columns are automatically parsed; use DuckDB date functions (DATE_TRUNC, EXTRACT, etc.)
• For very large files (100MB+), DuckDB handles them efficiently without loading everything into memory
• Column names with spaces are accessible using double quotes: "Column Name"