I recently needed to write a deduplicate method in a Rails app I built. In the application, each artist has_one song. However, over the course of several months, several songs had been added to the database with the same artist_id as an existing song.

Based on this helpful post, my deduplicate method looked like this:

Deduplicating Records with the Same Parent ID 1 2 3 4 5 6 7 8 class Song def self . deduplicate grouped = all . group_by { | song | song . artist_id } grouped . values . each do | artist_songs | first_one = artist_songs . shift artist_songs . each { | dup | dup . destroy } end end

This method groups every song by the song’s artist. For groupings with more than one song (i.e. songs that have the same artist_id ), it keeps the first song and deletes all the rest.

This works great, but it naively decides which duplicate record to destroy and which to keep.

To make the deduplicating method “smarter” we can use sort and sort_by to influence which duplicate will be kept. For example, if we wanted to keep the duplicate song with the highest play count, we could add this line before the shift method call:

1 artist_songs . sort! { | a , b | b . play_count <=> a . play_count }

This would ensure that the song “kept” using the shift method is the song with the highest play count.

It’s also possible to sort records by boolean values using sort_by . This was useful for my method, because in cases where an artist had two songs, I preferred to keep the song that had been reviewed by a trusted editor vs. one that had not.

The sort method doesn’t work with booleans, so we instead use sort_by and replace the booleans with integers to achieve the sort. I used the following line of code before the shift call:

1 artist_songs . sort_by! { | song | song . reviewed ? 0 : 1 }

Now, I have a concise, reusable method I can use to intelligently de-duplicate my songs.

Charles Worthington (@cew821) is a freelance product designer living in Washington, DC. He would love to hear from you!