ja: The JSONL Algebra Toolkit 🚀

Your friendly, powerful command-line tool for wrangling JSONL data.

Tired of wrestling with complex JSON in the command line? ja is here to help. It brings the power of relational algebra to your terminal, making it effortless to slice, dice, and transform streams of JSONL data. Think of it as sed, awk, and SQL rolled into one, but designed specifically for the structure and complexity of modern JSON.

Key Features

• Intuitive Relational Operations: All the classics are here: select, project, join, union, difference, distinct, and more.
• Seamless Nested Data Support: Access and manipulate nested fields using simple, intuitive dot notation (e.g., user.address.city). This is a core design principle.
• Powerful Aggregations: Group your data with groupby and calculate sum, avg, min, max, count, or see all values in a list.
• Interactive REPL: Jump into an interactive session with ja repl to explore and transform data interactively with named datasets and immediate execution.
• Schema Inference & Validation: Automatically discover the schema of your data with schema infer and validate it against a known structure.
• Format Conversion: Easily convert data to and from CSV, including intelligent flattening of nested structures.
• Built for Pipes: ja is a good Unix citizen. It reads from stdin, writes to stdout, and is designed to be a component in larger shell pipelines.

Getting Started: A 5-Minute Tour

Let’s see how ja can solve a real-world problem. Imagine you have two data files: users.jsonl and orders.jsonl.

users.jsonl

{"user": {"id": 1, "name": "Alice"}}
{"user": {"id": 2, "name": "Bob"}}

orders.jsonl

{"order_id": 101, "customer_id": 1, "amount": 50}
{"order_id": 102, "customer_id": 1, "amount": 75}
{"order_id": 103, "customer_id": 2, "amount": 120}

Goal: Find the total amount spent by each user.

Step 1: Join the Datasets

First, we’ll join the two files. Notice how we can reach into the nested user object with user.id to connect it to the customer_id in the orders file.

ja join users.jsonl orders.jsonl --on user.id=customer_id

This command produces a stream of the combined data:

{"user": {"id": 1, "name": "Alice"}, "order_id": 101, "customer_id": 1, "amount": 50}
{"user": {"id": 1, "name": "Alice"}, "order_id": 102, "customer_id": 1, "amount": 75}
{"user": {"id": 2, "name": "Bob"}, "order_id": 103, "customer_id": 2, "amount": 120}

Step 2: Group and Sum

Now, we can pipe (|) the result of our join directly into the groupby command. We’ll group by the user’s name and ask for the sum of the amount field.

ja join users.jsonl orders.jsonl --on user.id=customer_id \
  | ja groupby user.name --agg sum:amount

Final Result:

{"user.name": "Alice", "sum_amount": 125}
{"user.name": "Bob", "sum_amount": 120}

And there you have it! A sophisticated data transformation performed with a clear, readable command-line pipeline.

Installation

Installing ja is as simple as a single pip command.

pip install jsonl-algebra

This gives you the ja command-line tool and the Python library.

Core Concepts

Dot Notation for Nested Data

You can access nested values in any command by separating keys with a dot.

project: ja project user.name,user.address.city ...

select: ja select 'user.age > 30' ...

join: ja join ... --on user.id=order.user_id

groupby: ja groupby user.location ...

Streaming and Piping

Every ja command that processes a single stream of data can read from stdin and writes to stdout. This lets you build powerful workflows by chaining commands together with the standard Unix pipe (|).

cat data.jsonl | ja select ... | ja groupby ... | ja sort ...

CLI Command Examples

Here are a few quick examples of common commands.

Filtering Data

# Select rows where the 'status' field is 'active'
ja select 'status == `"active"`' data.jsonl

# Select rows where a nested 'age' is over 30
ja select 'user.age > 30' data.jsonl

Reshaping Data

# Pick only the 'id' and 'name' fields
ja project id,name data.jsonl

# Rename 'id' to 'user_id' and a nested 'loc' to 'location'
ja rename id=user_id,user.loc=user.location data.jsonl

Grouping and Aggregating

# Group by category and get the count for each
ja groupby category --agg count data.jsonl

# Group by location and find the average score
ja groupby location --agg avg:score data.jsonl

Working with Schemas

# Automatically infer a JSON Schema from your data
ja schema infer my_data.jsonl > my_schema.json

# Validate that a file conforms to a schema
ja schema validate my_schema.json my_data.jsonl

Interactive REPL

The REPL provides an interactive workspace for data exploration and transformation:

# Start the REPL
ja repl

# Or load a file immediately
ja repl users.jsonl

Example REPL Session:

ja> load users.jsonl
Loaded: users (current)

ja> select 'age > 30' adults
Created: adults (current)

ja> info
Dataset: adults
Rows: 15
Size: 2.3 KB
Fields: id, name, age, email, city

ja> load orders.jsonl
Loaded: orders (current)

ja> cd adults
Current dataset: adults

ja> join orders --on id=user_id user_orders
Created: user_orders (current)

ja> sort amount --desc sorted
Created: sorted (current)

ja> ls --limit 5
{"id": 1, "name": "Alice", "age": 35, "order_id": 101, "amount": 1200}
...

ja> save results.jsonl
Saved sorted to: results.jsonl

REPL Commands:

• load <file> [name] - Load a JSONL file
• cd <name> - Switch to a dataset
• datasets - List all loaded datasets
• info [name] - Show dataset statistics
• ls [--limit N] - Preview data
• All operations: select, project, join, groupby, etc. (require output name)
• !<command> - Execute shell commands
• save <file> - Persist current dataset

Programmatic API Usage

You can also use ja as a Python library to bring its power into your scripts.

from ja.core import read_jsonl, join, groupby_agg
from ja.schema import infer_schema

# Load data from JSONL files
users = read_jsonl("users.jsonl")
orders = read_jsonl("orders.jsonl")

# Join the data on the user ID
joined_data = join(users, orders, on=[("user.id", "customer_id")])

# Group by user name and sum the order amounts
# The result is an iterator, so we wrap it in list() to print.
result = groupby_agg(
    joined_data,
    group_by_key="user.name",
    aggregations=[("sum", "amount")]
)

print(list(result))
# Output:
# [{'user.name': 'Alice', 'sum_amount': 125},
#  {'user.name': 'Bob', 'sum_amount': 120}]

# You can also infer a schema directly
users_schema = infer_schema(users)
print(users_schema)

Contributing

Contributions are welcome! Please feel free to submit a pull request or open an issue.

License

This project is licensed under the MIT License.