Strings and Integers

Ruby has two powerful classes called String and Fixnum with lots of built-in power.

• Strings are enclosed by 'single' or "double" quotes.
• Strings have a number of methods, like .upcase, .reverse, and .length which are very helpful. Full documentation of String methods can be found here.
• String characters can be accessed using bracket notation. For example, the first character in my_string could be accessed using my_string[0].
• A string can be converted to an array using the .split() method (and back again to a string using .join()!)
• The Fixnum class contains all the operators like +, -, *, and / that you would use for basic arithmetic.
• The modulo (%) operator returns the remainder of a number divided by another and is helpful for creating Boolean conditionals and controlling the flow of a program.
• You can also check whether an integer is even or odd using .even? and .odd?. These methods return the Boolean value of true or false.

Arrays

Arrays are ordered sets of data that can be manipulated in a variety of helpful ways.

Elements in an array are given index numbers which correspond to their order. Index numbering starts at 0, so the first element of my_array would be accessed like so: my_array[0].

There are a huge number of helpful methods you can call on arrays. These include .length, .reverse, and .sort. The full documentation can be found here.

Looping through an array is easy with the .each method. This method takes a code block which it will apply to each element in the array.

The power of arrays is extended even further with the Enumerable Module mixed in. Enumberable provides a comprehensive toolkit for manipulating and iterating over arrays. Documentation can be found here.

Arrays can be one-dimensional or multi-dimensional. An array that contains arrays is called a nested array. You can access the elements inside the inner array by using stacked indices. my_array[2][0] would return the first element inside the third array inside my_array.

Arrays have destructive methods that end with a bang: !. These methods (like sort!) will permanently alter the original array object. The non-destructive versions will leave the original object as it was and create a new object that has been manipulated by the given code block.

Hashes

Hashes are data sets organized by key/pair values.

Any object can be used as a hash key, but the most common keys are strings and symbols.

Like arrays, hashes have a number of powerful methods that let the user manipulate and explore them. Methods like has_key?, .length, and .any permit a user to peer inside the hash. Full documentation is found here.

Also like Arrays, Hashes include the Enumerable Module, which give users a great deal of power to iterate over and manipulate their hashes.

Hashes values are accessed using the key. For example, my_hash[key] would output the value associated with that key.

Adding a new value to a hash is as simple as using the hash name, with the key name in brackets, and setting it equal to the value. For example: my_hash[:key] = new_value.

Hashes can be looped through using the .each method, which takes both key and value as arguments and applies a given code block to each pair.