An unordered group_by implementation that is a lot faster than the ordered version used in ActiveSupport version 2.2.x. This becomes apparent when used with large data sets.
How to install
When you have setup gemcutter.org as a gem source, you can install it with:
sudo gem install fast_group_by
When you have setup gems.github.com as a gem source, you can install it with:
sudo gem install Narnach-fast_group_by
If you want tests, benchmarks and the project's history, you can clone the git repo and build the gem yourself:
git clone git://github.com/Narnach/fast_group_by.git cd fast_group_by rake install
ActiveSupport uses OrderedHash in its Enumerable#group_by. In version 2.2.x, it uses nested Arrays to store data. Array#assoc is used to find if keys are already defined. For small Arrays, Array#assoc's linear search is about as fast as Hash#' tree search, but for larger data sets, the difference in lookup speed becomes noticeable. In version 2.3.x, there is a new implementation of OrderedHash that uses Hash instead of Array and is thus a lot faster. Using fast_group_by with ActiveSupport 2.3.x does not make much sense.
The reason why I wrote this is that the OrderedHash version took 66 seconds to group a collection of 50k items. The Hash version took less than 1 second.
Copyright © 2009 Wes Oldenbeuving
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