Ruby Cookbook

Recipe 4.1. Iterating Over an Array Problem You want to perform some operation on each item in an array. Solution Iterate over the array with Enumerable#each. Put into a block the code you want to execute for each item in the array. ...

Recipe 4.2. Rearranging Values Without Using Temporary Variables Problem You want to rearrange a number of variables, or assign the elements of an array to individual variables. Solution Use a single assignment statement. Put the des...

Recipe 4.3. Stripping Duplicate Elements from an Array Problem You want to strip all duplicate elements from an array, or prevent duplicate elements from being added in the first place. Solution Use Array#uniq to create a new arra...

Recipe 4.4. Reversing an Array Problem Your array is the wrong way around: the last item should be first and the first should be last. Solution Use reverse to create a new array with the items reversed. Internal subarrays will not...

Recipe 4.5. Sorting an Array Problem You want to sort an array of objects, possibly according to some custom notion of what "sorting" means. Solution Homogeneous arrays of common data types, like strings or numbers, can be sorted ...

Recipe 4.6. Ignoring Case When Sorting Strings Problem When you sort a list of strings, the strings beginning with uppercase letters sort before the strings beginning with lowercase letters. list = ["Albania", "anteater", "zorilla", "Z...

Recipe 4.7. Making Sure a Sorted Array Stays Sorted Problem You want to make sure an array stays sorted, even as you replace its elements or add new elements to it. Solution Subclass Array and override the methods that add items to the ar...

Recipe 4.8. Summing the Items of an Array Problem You want to add together many objects in an array. Solution There are two good ways to accomplish this in Ruby. Plain vanilla iteration is a simple way to approach the problem: co...

Recipe 4.9. Sorting an Array by Frequency of Appearance Problem You want to sort an array so that its least-frequently-appearing items come first. Solution Build a histogram of the frequencies of the objects in the array, then u...

Recipe 4.10. Shuffling an Array Problem You want to put the elements of an array in random order. Solution The simplest way to shuffle an array (in Ruby 1.8 and above) is to sort it randomly: [1,2,3].sort_by { rand } # => [1,...

Recipe 4.11. Getting the N Smallest Items of an Array Problem You want to find the smallest few items in an array, or the largest, or the most extreme according to some other measure. Solution If you only need to find the singl...

Recipe 4.12. Building Up a Hash Using Injection Problem You want to create a hash from the values in an array. Solution As seen in Recipe 4.8, the most straightforward way to solve this kind of problem is to use Enumerable#inject....

Recipe 4.13. Extracting Portions of Arrays Problem Given an array, you want to retrieve the elements of the array that occupy certain positions or have certain properties. You might to do this in a way that removes the matching elements ...

Recipe 4.14. Computing Set Operations on Arrays Problem You want to find the union, intersection, difference, or Cartesian product of two arrays, or the complement of a single array with respect to some universe. Solution Array objec...