The bisect gem provides helpers for dealing with sorted Arrays. It uses binary search to reduce the number of comparisons that need to be run.

gem install bisect

If you're using Bundler, add gem 'bisect' to your Gemfile.

There are two functions that you need to know about Bisect.insort and Bisect.bisect.

Bisect.insort adds a new element to the Array, but keeps the Array sorted:

require 'bisect'
a = [1, 2, 4]
Bisect.insort(a, 3)
a == [1, 2, 3, 4]

Bisect.bisect gives you the index at which the element would have been inserted:

require 'bisect'
a = ['a', 'b', 'd']
Bisect.bisect(a, 'c') == 2

If there are equal elements in the Array then insort will insert the element after the last equal element. Similarly bisect will return the index one higher than the last equal element. If you'd like to add new elements before equal elements, use insort_left and bisect_left. If you need to be explicit then insort_right and bisect_right are aliases for insort and bisect.

If you want these methods in your Arrays by default, require 'bisect/core_ext' If you're using bundler, add gem 'bisect', :require => 'bisect/core_ext' to your Gemfile.

require 'bisect/core_ext'
a = [1, 2, 4]
a.insort(3)
a == [1, 2, 3, 4]

The problem of maintaining a sorted array keeps cropping up, and I like the Python API. As this kind of code has lots of edge-cases, I'm glad the Pythonistas have debugged it already.

• Add a subclass of Array that magically stays sorted.

Licensed under the MIT license, bug reports and pull requests welcome.