Welcome to today's session on "Multidimensional Arrays and Their Traversal in Ruby". Multidimensional arrays are types of arrays that store arrays at each index instead of single elements. Picture it as an 'apartment building' with floors (the outer array) and apartments on each floor (the inner array). Our goal today is to strengthen your foundational knowledge of these 'apartment buildings' and how to handle them effectively in Ruby.

To construct a multidimensional or nested array in Ruby, we use arrays inside arrays. Here's an example of a 2-dimensional array:

In this example, array is a 2-dimensional array, just like a 3-story 'apartment building,' where every floor is an inner array.

All indices in Ruby arrays are 0-based. Let's say you want to visit an apartment on the second floor (index 1) and bring a package to the first unit (index 0) in this building. Here's how you can do it:

We visited the element 4 in the array by its position. The number 1 inside the first square brackets refers to the second inner array, and refers to the first element of that array.