lanicemp/programming-univbasics-4-crud-lab-online-web-prework

Array Lab: Create, Retrieve, Update, Delete

Learning Goals

• Create a new array that contains data as well as a new array that is empty
• Add an element to the end of an array
• Add an element to the front of an array
• Remove an element from the front of an array
• Remove an element from the end of an array
• Retrieve data from a specific array index
• Update an element value using its index number

Introduction

In this lab, you will create arrays, add data to arrays, remove data from arrays and retrieve data from arrays.

We will be coding the solutions for each of the above tasks in the body of a method. In lib/array_crud.rb we've defined a series of methods for you, each of which is responsible for one of the tasks above.

Let's go through the first challenge together.

create_an_empty_array

Let's run our test suite to get started. Run the tests one at a time with the learn --fail-fast command in your terminal.

If we do so, we'll see our first failure:

Our test is telling us that we are expected to code the content of our create_an_empty_array method such that a new, empty array is created and returned. Our test expected an empty array, [], but got nil.

Open up lib/array_crud.rb and check out the create_an_empty_array method. It's empty! Let's write the code that will get the test passing.

We'll use the literal constructor to make a new array with nothing in it:

def create_an_empty_array
  []
end

Run the test suite again and we should be passing that first test.

create_an_array

This method should use the literal constructor to create a new array, just like we did above. This time, however, create an array that contains four elements. The four elements can be any elements of your choosing, as long as there are only four of them.

add_element_to_end_of_array

This method takes in two arguments, an array and the element we want to add to it. Use the << (shovel) method or the push method to add that element to the end of the new array.

add_element_to_start_of_array

This method takes in two arguments, an array and the element we want to add to it. Use the unshift method to add that element to the start of that array.

remove_element_from_end_of_array

This method takes in one argument, the array on which we want to operate. Use the pop method to remove the last item from the array.

remove_element_from_start_of_array

This method takes in one argument, the array on which we want to operate. Use the shift method to remove the first item from the array.

retrieve_element_from_index

This method takes in two arguments, an array and the index number whose element we want to retrieve. Use the [], bracket method to return the element stored at that index number of the given array.

retrieve_first_element_from_array

This method takes in one argument, the array from which we want to retrieve an element. Use [] notation to return the value stored at the first index of the array. Remember that arrays are zero-indexed. This means that the first index number is 0 and it counts up from there. So, the first element of an array is stored at index 0.

retrieve_last_element_from_array

This method takes in one argument, the array from which we want to retrieve an element. There are a number of ways to do this, but we recommend using the [] method with the following hint:

The last element of an array is considered to be stored at an index of -1.

update_element_from_index

This method takes in three arguments: the array from which we want to update an element, the index number of the element to update and the new element value. Refer back to your retrieve_element_from_index method for how to target the desired element.

Conclusion

Congratulations! You just completed learning how to work with create, retrieve, update, and delete array operations using simple operations provided to us in Ruby.