A Case for Learning J

There are few things as humbling as learning a programming language of a radically different paradigm from any you’ve used before. Recently, I’ve been feeling a need to learn a language with which I could easily manipulate data – usually collections of numbers. I thought about learning R or Julia, but while I’m sure those systems are extremely useful, they didn’t seem to offer the chance to have my world rocked and my conception of reality turned upside down. As long as I’m going to learn a language for practical reasons, I might as well learn a Perlis language that will show me (once again) just how much I have to learn about software, so I decided to learn J.

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Using ActiveRecord to Abstract “Greatest N Per Group” Queries

Some database-related projects require access to information based around maximum and minimum values. Recently, I was trying to figure out the best way to perform a “greatest N per group” query in an ActiveRecord model with a SQL database backend. Eventually, I settled on the SQL proposed by Bill Karwin on StackOverflow. Once I had the SQL, I worked it into a form that fit my needs and moved it into my ActiveRecord model.

My approach allowed me to specify the group based on a set of columns and to abstract the required join logic behind an ActiveRecord scope. The following gist is a complete script that demonstrates the approach.

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