Fractional Indexing
This is based on Implementing Fractional Indexing by David Greenspan .
Fractional indexing is a technique to create an ordering that can be used for Realtime Editing of Ordered Sequences.
This implementation includes variable-length integers, and the prepend/append optimization described in David's article.
Installation
Install the gem and add to the application's Gemfile by executing:
$ bundle add fractional_indexing
If bundler is not being used to manage dependencies, install the gem by executing:
$ gem install fractional_indexing
Usage
require "fractional_indexing"
first = FractionalIndexing.generate_key_between(None, None)
raise unless first == 'a0'
# Insert after 1st
second = FractionalIndexing.generate_key_between(first, None)
raise unless second == 'a1'
# Insert after 2nd
third = FractionalIndexing.generate_key_between(second, None)
raise unless third == 'a2'
# Insert before 1st
zeroth = FractionalIndexing.generate_key_between(None, first)
raise unless zeroth == 'Zz'
# Insert in between 2nd and 3rd. Midpoint
second_and_half = FractionalIndexing.generate_key_between(second, third)
raise unless second_and_half == 'a1V'Other Languages
This is a Ruby port of the Python port of the original JavaScript implementation. That means that this implementation is byte-for-byte compatible with:
| Language | Repo |
|---|---|
| JavaScript | https://github.com/rocicorp/fractional-indexing |
| Go | https://github.com/rocicorp/fracdex |
| Python | https://github.com/httpie/fractional-indexing-python |
The code was ported entirely by ChatGPT.