json-flattener

Python library for denormalizing/flattening lists of complex objects to tables/data frames, with roundtripping

Notebook Example

Description

Given YAML/JSON/JSON-Lines such as:

- id: S001
  name: Lord of the Rings
  genres:
    - fantasy
  creator:
    name: JRR Tolkein
    from_country: England
  books:
    - id: S001.1
      name: Fellowship of the Ring
      price: 5.99
      summary: Hobbits
    - id: S001.2
      name: The Two Towers
      price: 5.99
      summary: More hobbits
    - id: S001.3
      name: Return of the King
      price: 6.99
      summary: Yet more hobbits
- id: S002
  name: The Culture Series
  genres:
    - scifi
  creator:
    name: Ian M Banks
    from_country: Scotland
  books:
    - id: S002.1
      name: Consider Phlebas
      price: 5.99
    - id: S002.2
      name: Player of Games
      price: 5.99

Denormalize using jfl command:

jfl flatten -C creator=flat -C books=multivalued -i examples/books1.yaml -o examples/books1-flattened.tsv

id	name	genres	creator_name	creator_from_country	books_name	books_summary	books_price	books_id	creator_genres
S001	Lord of the Rings	[fantasy]	JRR Tolkein	England	[Fellowship of the Ring\|The Two Towers\|Return of the King]	[Hobbits\|More hobbits\|Yet more hobbits]	[5.99\|5.99\|6.99]	[S001.1\|S001.2\|S001.3]
S002	The Culture Series	[scifi]	Ian M Banks	Scotland	[Consider Phlebas\|Player of Games]		[5.99\|5.99]	[S002.1\|S002.2]

Convert back to JSON/YAML:

jfl unflatten -C creator=flat -C books=multivalued -i examples/books1.tsv -o examples/books1.yaml

This library also allows complex fields to be directly serialized as json or yaml (the default is to append _json to the key). For example:

jfl flatten -C creator=json -C books=json -i examples/books1.yaml -o examples/books1-jsonified.tsv

id	name	genres	creator_json	books_json
S001	Lord of the Rings	[fantasy]	{"name": "JRR Tolkein", "from_country": "England"}	[{"id": "S001.1", "name": "Fellowship of the Ring", "summary": "Hobbits", "price": 5.99}, {"id": "S001.2", "name": "The Two Towers", "summary": "More hobbits", "price": 5.99}, {"id": "S001.3", "name": "Return of the King", "summary": "Yet more hobbits", "price": 6.99}]
S002	The Culture Series	[scifi]	{"name": "Ian M Banks", "from_country": "Scotland"}	[{"id": "S002.1", "name": "Consider Phlebas", "price": 5.99}, {"id": "S002.2", "name": "Player of Games", "price": 5.99}]
S003	Book of the New Sun	[scifi, fantasy]	{"name": "Gene Wolfe", "genres": ["scifi", "fantasy"], "from_country": "USA"}	[{"id": "S003.1", "name": "Shadow of the Torturer"}, {"id": "S003.2", "name": "Claw of the Conciliator", "price": 6.99}]
S004	Example with single book		{"name": "Ms Writer", "genres": ["romance"], "from_country": "USA"}	[{"id": "S004.1", "name": "Blah"}]
S005	Example with no books		{"name": "Mr Unproductive", "genres": ["romance", "scifi", "fantasy"], "from_country": "USA"}

See

The primary use case is to go from a rich normalized data model (as python objects, JSON, or YAML) to a flatter representation that is amenable to processing with:

Solr/Lucene
Pandas/R Dataframes
Excel/Google sheets
Unix cut/grep/cat/etc
Simple denormalized SQL database representations

The target denormalized format is a list of rows / a data matrix, where each cell is either an atom or a list of atoms.

Method

Each top level key becomes a column
if the key value is a dict/object, then flatten
- by default a '_' is used to separate the parent key from the inner key
- e.g. the composition of creator and from_country becomes creator_from_country
- currently one level of flattening is supported
if the key value is a list of atomic entities, then leave as is
if the key value is a list of dicts/objects, then flatten each key of this inner dict into a list
- e.g. if books is a list of book objects, and name is a key on book, then books_name is a list of names of each book
- order is significant - the first element of books_name is matched to the first element of books_price, etc
Allow any key to be serialized as yaml/json/pickle if configured

Command line usage (TODO)

Usage from Python

Documentation coming soon: see test folder for now

use within LinkML

Comparison

Pandas json_normalize

https://pandas.pydata.org/pandas-docs/version/0.25.0/reference/api/pandas.io.json.json_normalize.html

dalito/json-flattener