Median and percentile for Active Record, Mongoid, arrays, and hashes

Supports:

• PostgreSQL 9.4+
• MariaDB 10.3.3+
• MySQL and SQL (with extensions)
• SQL Server 2012+
• MongoDB 2.1+

🔥 Uses native functions for blazing performance

Add this line to your application’s Gemfile:

gem 'active_median'

For MySQL and SQLite, also follow these instructions.

Median

Item.median(:price)

Percentile

Request.percentile(:response_time, 0.95)

Works with grouping, too

Order.group(:store_id).median(:total)

If passing user input as the column, be sure to sanitize it first like you must with other aggregate methods like sum.

column = params[:column]

# check against permitted columns
raise "Unpermitted column" unless ["column_a", "column_b"].include?(column)

User.median(column)

Median

[1, 2, 3].median

Percentile

[1, 2, 3].percentile(0.95)

You can also pass a block

{a: 1, b: 2, c: 3}.median { |k, v| v }

MySQL requires the PERCENTILE_CONT function from udf_infusion. To install it, do:

git clone https://github.com/infusion/udf_infusion.git
cd udf_infusion
./configure --enable-functions="percentile_cont"
make
sudo make install
mysql <options> < load.sql

SQLite requires a community extension. Download extension-functions.c and follow the instructions for compiling loadable extensions for your platform. On Mac, use:

gcc -g -fPIC -dynamiclib extension-functions.c -o extension-functions.dylib

To load it in Rails, create an initializer with:

db = ActiveRecord::Base.connection.raw_connection
db.enable_load_extension(1)
db.load_extension("extension-functions.dylib")
db.enable_load_extension(0)

A user-defined function is no longer needed for Postgres. Create a migration with ActiveMedian.drop_function to remove it.

Everyone is encouraged to help improve this project. Here are a few ways you can help:

• Report bugs
• Fix bugs and submit pull requests
• Write, clarify, or fix documentation
• Suggest or add new features

To get started with development and testing:

git clone https://github.com/ankane/active_median.git
cd active_median
createdb active_median_test
bundle install
bundle exec rake test