Over a million developers have joined DZone.
{{announcement.body}}
{{announcement.title}}

Clojure: Destructuring Group-by's Output

DZone's Guide to

Clojure: Destructuring Group-by's Output

· DevOps Zone ·
Free Resource

Learn more about how CareerBuilder was able to resolve customer issues 5x faster by using Scalyr, the fastest log management tool on the market. 

One of my favourite features of Clojure is that it allows you to destructure a data structure into values that are a bit easier to work with.

I often find myself referring to Jay Fields’ article which contains several examples showing the syntax and is a good starting point.

One recent use of destructuring I had was where I was working with a vector containing events like this:

user> (def events [{:name "e1" :timestamp 123} {:name "e2" :timestamp 456} {:name "e3" :timestamp 789}])

I wanted to split the events in two – those containing events with a timestamp greater than 123 and those less than or equal to 123.

After remembering that the function I wanted was group-by and not partition-by (I always make that mistake!) I had the following:

user> (group-by #(> (->> % :timestamp) 123) events)
{false [{:name "e1", :timestamp 123}], true [{:name "e2", :timestamp 456} {:name "e3", :timestamp 789}]}

I wanted to get 2 vectors that I could pass to the web page and this is fairly easy with destructuring:

user> (let [{upcoming true past false} (group-by #(> (->> % :timestamp) 123) events)] 
       (println upcoming) (println past))
[{:name e2, :timestamp 456} {:name e3, :timestamp 789}]
[{:name e1, :timestamp 123}]
nil

Simple!

Find out more about how Scalyr built a proprietary database that does not use text indexing for their log management tool.

Topics:

Published at DZone with permission of

Opinions expressed by DZone contributors are their own.

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}