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
Once the gem appears on gems.github.com, you can install it with:
sudo gem install Narnach-fast_group_by
The alternative is to 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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