Ruby Cookbook

Recipe 2.1. Parsing a Number from a String Problem Given a string that contains some representation of a number, you want to get the corresponding integer or floating-point value. Solution Use String#to_i to turn a string into an ...

Recipe 2.2. Comparing Floating-Point Numbers Problem Floating-point numbers are not suitable for exact comparison. Often, two numbers that should be equal are actually slightly different. The Ruby interpreter can make seemingly nonse...

Recipe 2.3. Representing Numbers to Arbitrary Precision Problem You're doing high- precision arithmetic, and floating-point numbers are not precise enough. Solution A BigDecimal number can represent a real number to an arbitrary nu...

Recipe 2.4. Representing Rational Numbers Problem You want to precisely represent a rational number like 2/3, one that has no finite decimal expansion. Solution Use a Rational object; it represents a rational number as an integ...

Recipe 2.5. Generating Random Numbers Problem You want to generate pseudorandom numbers, select items from a data structure at random, or repeatedly generate the same "random" numbers for testing purposes. Solution Use the Kernel#rand ...

Recipe 2.6. Converting Between Numeric Bases Problem You want to convert numbers from one base to another. Solution You can convert specific binary, octal, or hexadecimal numbers to decimal by representing them with the 0b, 0o, or 0x...

Recipe 2.7. Taking Logarithms Problem You want to take the logarithm of a number, possibly a huge one. Solution Math.log calculates the natural log of a number: that is, the log base e. Math.log(1) # =...

Recipe 2.8. Finding Mean, Median, and Mode Problem You want to find the average of an array of numbers: its mean, median, or mode. Solution Usually when people speak of the "average" of a set of numbers they're referr...

Recipe 2.9. Converting Between Degrees and Radians Problem The trigonometry functions in Ruby's Math library take input in radians (2π radians in a circle). Most real-world applications measure angles in degrees (360 degrees in ...

Recipe 2.10. Multiplying Matrices Problem You want to turn arrays of arrays of numbers into mathematical matrices, and multiply the matrices together. Solution You can create Matrix objects from arrays of arrays, and multiply ...

Recipe 2.11. Solving a System of Linear Equations Problem You have a number of linear equations (that is, equations that look like "2x + 10y + 8z = 54"), and you want to figure out the solution: the values of x, y, and z. You have as many...

Recipe 2.12. Using Complex Numbers Problem You want to represent complex ("imaginary") numbers and perform math on them. Solution Use the Complex class, defined in the complex library. All mathematical and trigonometric operat...

Recipe 2.13. Simulating a Subclass of Fixnum Problem You want to create a class that acts like a subclass of Fixnum, Float, or one of Ruby's other built-in numeric classes. This wondrous class can be used in arithmetic along with real Int...

Recipe 2.14. Doing Math with Roman Numbers Problem You want to convert between Arabic and Roman numbers, or do arithmetic with Roman numbers and get Roman numbers as your result. Solution The simplest way to define a Roman class tha...

Recipe 2.15. Generating a Sequence of Numbers Problem You want to iterate over a (possibly infinite) sequence of numbers the way you can iterate over an array or a range. Solution Write a generator function that yields each number i...

Recipe 2.16. Generating Prime Numbers Problem You want to generate a sequence of prime numbers, or find all prime numbers below a certain threshold. Solution Instantiate the Prime class to create a prime number generator. C...