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10 ruby one liners

June 2, 2011

The following blog entry is pasted from here:

Multiply each item in a list by 2

(1..10).map { |n| n * 2 }

Sum a list of numbers

(1..1000).inject { |sum, n| sum + n }

Or using the Symbol#to_proc syntax available (built-in) since Ruby 1.8.7:


Or even just passing a symbol directly:


Verify if tokens exist in a string

words = ["scala", "akka", "play framework", "sbt", "typesafe"]
tweet = "This is an example tweet talking about scala and sbt."

words.any? { |word| tweet.include?(word) }

Reading a file

file_text ="data.txt")
file_lines = File.readlines("data.txt")

The latter includes “\n” at the end of each element of the array, which can be trimmed by appending .map { |str| str.chop } or by using the alternative version:"data.txt").split(/\n/)

Happy Birthday

4.times { |n| puts "Happy Birthday #{n==2 ? "dear Tony" : "to You"}" }

Filter a list of numbers

[49, 58, 76, 82, 88, 90].partition { |n| n > 60 }

Fetch and parse an XML web service

require 'open-uri'
require 'hpricot'

results = Hpricot(open(""))

This example requires open-uri and hpricot or equivalent libraries (you could use builtin ones if you wish). It’s not too much code, but Scala clearly wins here.

Find minimum (or maximum) in a list

[14, 35, -7, 46, 98].min
[14, 35, -7, 46, 98].max

Parallel Processing

require 'parallel' do |chunk|

Unlike Scala, multicore support is not built-in. It requires parallel or a similar gem.

Sieve of Eratosthenes

The Scala one liner is very clever, but entirely unreadable. A simpler implementation that is no longer a one-liner in Ruby would be:

index = 0
while primes[index]**2 <= primes.last
      prime = primes[index]
      primes = { |x| x == prime || x % prime != 0 }
      index += 1
p primes

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One Comment
  1. Hi Antonio,

    I am the one who wrote the unreadable article you mention 🙂

    Regular expressions are just very complex to explain. Especially /^1?$|^(11+?)\1+$/ which, for some people, including myself initially, which looks more like a bunch of random symbols than something meaningful 🙂

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