11.11. Studio: More Functions

11.11.1. Before You Start

If you are enrolled in a LaunchCode program, access this studio by following the repl.it classroom links posted in your class at learn.launchcode.org.

If you are working through this material on your own, use the repl.it links contained on this page.

11.11.2. Sort Numbers For Real

Recall that using the sort method on an array of numbers produced an unexpected result, since JavaScript converts the numbers to strings by default. Let's fix this!

Here is one approach to sorting an array:

  1. Find the minimum value in an array,
  2. Add that value to a new array,
  3. Remove the entry from the old array,
  4. Repeat steps 1 - 3 until the numbers are all in order.

11.11.2.1. Part A: Find the Minimum Value

Create a function with an array of numbers as its parameter. The function should iterate through the array and return the minimum value from the array.

Hint: Use what you know about if statements to identify and store the smallest value within the array.

Tip

Use this sample data for testing.

1
2
3
[ 5, 10, 2, 42 ]
[ -2, 0, -10, -44, 5, 3, 0, 3 ]
[ 200, 5, 4, 10, 8, 5, -3.3, 4.4, 0 ]

Code studio part A at repl.it.

11.11.2.2. Part B: Create a New Sorted Array

Create another function with an array of numbers as its parameter. Within this function:

  1. Define a new, empty array to hold the final sorted numbers.
  2. Use your function from the previous exercise to find the minimum value in the old array.
  3. Add the minimum value to the new array, and remove the minimum value from the old array.
  4. Repeat parts b & c until the old array is empty.
  5. Return the new sorted array.
  6. Be sure to print the results in order to verify your code.

Code studio part B at repl.it.

Tip

Which type of loop?

Either a for or while loop will work inside this function, but one IS a better choice. Consider what the function must accomplish vs. the behavior of each type of loop. Which one best serves if the array has an unknown length?

11.11.3. More on Sorting Numbers

The sorting approach used above is an example of a selection sort. The function repeatedly checks an array for the minimum value, then places that value into a new container.

Selection sorting is NOT the most efficient way to accomplish the task, since it requires the function to pass through the array once for each item within the array. This takes way too much time for large arrays.

Fortunately, JavaScript has an elegant way to properly sort numbers.

Tip

Here is a nice, visual comparison of different sorting methods.

Feel free to Google "bubble sort JavaScript" to explore a different way to order numbers in an array.

11.11.4. Part C: Number Sorting the Easy Way

If you Google "JavaScript sort array of numbers" (or something similar), many options appear, and they all give pretty much the same result. The sites just differ in how much detail they provide when explaining the solution.

One reference is here: W3Schools.

End result: the JavaScript syntax for numerical sorting is arrayName.sort(function(a, b){return a-b});.

Here, the anonymous function determines which element is larger and swaps the positions if necessary. This is all that sort needs to order the entire array.

Using the syntax listed above:

  1. Sort each sample array in increasing order.
  2. Sort each sample array in decreasing order.
  3. Does the function alter arrayName?
  4. Did your sorting function from part B alter arrayName?

Code studio part C at repl.it.

11.11.5. So Why Write A Sorting Function?

Each programming language (Python, Java, C#, JavaScript, etc.) has built-in sorting methods, so why did we ask you to build one?

It's kind of a programming right of passage - design an efficient sorting function. Also, sorting can help you land a job.

As part of a tech interview, you will probably be asked to do some live-coding. One standard, go-to question is to sort an array WITHOUT relying on the built in methods. Knowing how to think though a sorting task, generate the code and then clearly explain your approach will significantly boost your appeal to an employer.

11.11.6. Bonus Mission

Refactor your sorting function from Part B to use recursion.