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Mastering Ruby Arrays

Ruby arrays are a fundamental data structure that is used to store data in memory. Inside a Ruby array you can store anything you want, from strings to integers and even other arrays. The elements in an array are accessed using their index, which starts at 0.

This is what an array containing the words “cat”, “dog” and “tiger” would look like:

ruby arrays

Ruby Arrays – Basic Operations

To work with an array you will have to create one first, there are multiple ways to do it.

Initialize an empty array:

Initialize an array with data:

Alternatively, you can avoid having to type the quotes for every string by doing this:

Now that we have an array the next step would be accessing the elements that it contains.

Access array element by index:

You can also use the first and last methods:

At this point you may want to add items to your array:

And finally, here is how you delete elements from your array:

There is also the shift & unshift methods, which are similar to pop/push but take or add elements in front of the array.

Here is a small cheatsheet for you:

Ruby Array to String

You can convert any array into a string by using the Array#join method.

Here’s an example:

Notice that this method takes 1 optional parameter so you can define a separator between the array elements when they are joined together.

Multidimensional Arrays

An array can be composed of other arrays, we call that a multi-dimensional array.

Example:

To access the first elements from the first sub-array you can use this syntax:

Iterating Over Ruby Arrays

Now that you have an array wouldn’t it be nice if you could enumerate its contents and print them? Well the good news is that you can!

Example: Print your array using each

Note: Most of these looping operations are available thanks to the Enumerable module, which is mixed into the Array class by default.

Example: Capitalize every word in your Array using map.

The map method doesn’t modify the array in-place, it just returns a new array with the modified elements, so we need to assign the results back to a variable. There is also a map! (notice the exclamation point) method which will modify the array directly, but in general the simpler version is preferred.

Another thing you may want to do is find all the items in your array that fit certain criteria.

Example: Find all the numbers greater than 10:

More Array Operations

There are a lot of things you can do using arrays, like sorting them or picking random elements.

You can use the sort method to sort an array, this will work fine if all you have is strings or numbers in your array. For more advanced sorting check out sort_by.

You can also remove the duplicate elements from an array, if you find yourself doing this often you may want to consider using a Set instead.

If you want to pick one random element from your array you can use the sample method:

You may also want to “slice” your array, taking a portion of it instead of the whole thing.

Example: Take the first 3 elements from the array, without changing it:

Get the size of an array:

Check if an array is empty:

Remove nil values:

Operations involving multiple arrays

If you have two arrays and want to join them you can do it like this.

You can also remove elements from one array like this, where users_to_delete is also an array:

Finally, you can get the elements that appear in two arrays at the same time:

Conclusion

Arrays are very useful and they will be a powerful ally by your side. Don’t forget to check out the documentation if you are unsure of what a method does.

If you found this useful please share this post & subscribe to my newsletter below πŸ™‚

10 comments
Dave Aronson says a couple of years ago

You’ve covered adding elements to the end of an array, and removing them from there, but ignored the front end, which is necessary in order to make a queue. There, you can use shift and unshift, respectively.

    Jesus Castello says a couple of years ago

    Thank you, I will add these πŸ™‚

    Jim OKelly (@rubycastsio) says a couple of years ago

    Wait to you get into any? none? each_cons and each_slice πŸ™‚

    Isn’t ruby an awesome language? Great write up, keep them coming!

      Jesus Castello says a couple of years ago

      Yeah, I love Ruby! Thanks for your comment πŸ™‚

Thiago AraΓΊjo says a couple of years ago

You can also use Array#shift instead of Array#delete_at(0), and use Array#slice instead of Array#[start, length]

Rick Carlino says a couple of years ago

Another fun one is reaching around arrays in the opposite direction with negative indexes. Example:

%w(1 2 3 4 5 6)[-2]

=> returns “5”

Ruby arrays really do give you a lot out-of-the-box when you compare it to other languages. Nice post!

    Jesus Castello says a couple of years ago

    Thanks for your comment πŸ™‚

richard (@richardkmichael) says a couple of years ago

#each_with_index, #each_with_object and #zip, all from Enumerable, are often helpful with arrays. Most people seem unaware of #zip, in particular.

Igor Zhivilo says a couple of years ago

good post, didn’t know about ‘numbers.take 3’ method, thanks

Sanju says a couple of years ago

Nice Article πŸ™‚

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