Jake Worth

Binary to Decimal Conversion in Ruby

May 04, 20172 min read

This week I wrote a small algorithm in Ruby to convert binary numbers into decimal numbers. Here’s the problem description, from Exercism.io:

Convert a binary number, represented as a string (e.g. ‘101010’), to its decimal equivalent using first principles. Implement binary to decimal conversion. Given a binary input string, your program should produce a decimal output. The program should handle invalid inputs.

And here is my code:

class Binary
  def self.to_decimal(string)
    raise ArgumentError if string.match?(/[^01]/)

    string.reverse.chars.map.with_index do |digit, index|
      digit.to_i * 2**index

Reading the Code

What’s going on here? Examining each line:

  1. We make a class Binary, a container for our code.
  2. We define a class method. Prefer functional when object instantiation isn’t beneficial.
  3. Guard clause! Raise an ArgumentError if the string does not match the binary format we expect.
  4. Space (let that code breathe).
  5. Reverse the string and split into characters, then map over each with index included.
  6. Take each digit (starting with the rightmost because we’ve reversed the string), convert it into a number, and multiply that number by two to the power of its enumerable index. In simpler terms, convert each digit to its binary value.
  7. Sum the result; close out the function and the class.

What’s Good

I like that my solution matches for ArgumentError positively, covering a range of bad inputs not specified by the test cases. I like that it reverses the string so that index can be used as the incrementing exponent. And, I like that it uses .map to return a result without an accumulator variable.

What I’d Do Differently Next Time

I do not love that my solution takes an argument called string. Although that’s the type the method expects, it doesn’t tell the reader a lot about what this method does. If I could rewrite it, I’d name that variable something like binary.

My solution is also a bit clever; I may have golfed this down a little too much. In general, I think mathematical functions can get away with terser syntax than ordinary functions, because the mathematical principles are easy to learn about with a quick Google search.


Thanks Exercism.io for this fun challenge, and thanks for reading! Here’s the permalink to my solution:

Binary to Decimal (Ruby)

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Jake Worth

I'm Jake Worth, a web developer. Home About Now Newsletter