PostgreSQL Histogram (for ActiveRecord)

This gem allows for you to efficiently create a histogram from large data sets in your Rails applications.

It uses PostgreSQL's width_bucket function to handle the majority of the processing in the database, and only requires 3 database queries.

Installation

Add this line to your application's Gemfile:

gem 'pg_histogram'

And then execute:

$ bundle

Or install it yourself as:

$ gem install pg_histogram

Usage

Create a Histogram object using the following three parameters:

  1. ActiveRecord query to use
  2. Name of column to count frequency of
  3. Bucket size (OPTIONAL - default is 0.5)
histogram = PgHistogram::Histogram.new(Widget.all, 'price', 0.5)

Call the results method to retrieve a Hash of bucket minimums and frequency counts

# create sample data
5.times do { Widget.create(price: 1.2) }
10.times do { Widget.create(price: 2.9 ) }

# get the results
@histogram_data = histogram.results
 => {1.0=>5, 2.5=>10}

The results can be used by your favorite charting libary, such as Chartkick, to plot the data.

<%= column_chart @histogram_data %>

Dependencies

This gem has been tested with Ruby 2.1.3 and ActiveRecord 4.1.6. Please open an issue or PR if you experience issues with other versions.