- Learn the
setdata type - Create a
setfrom alist - Discover the difference between
setandlist - Create a
setfrom our lyrics
A list can contain as many duplicates of each item as necessary, but sometimes we want a list of which unique items are in our list. We are able to do this with the set() function. The set() function creates a collection of all of the unique elements from the collection that is passed to it. Let's take a look at sets before we get back to our project.
A set is a collection of unique elements and is un-ordered and un-indexed. As an example the list [1, 2, 2, 4, 4, 5, 6] when converted to a set would result in the following set {1, 2, 4, 5, 6}.
Run the code console below and see for yourself how this works. Click on the green arrow to see the output from this code.
<iframe frameborder="0" width="100%" height="400px" src="https://repl.it/@DSExperience/ListandSet?lite=true"></iframe>One of the properties of a set is that the order of the elements in the set doesn't matter. What does that mean? Let's look at a simple example. set_1 and set_2 below are two sets, each contains the same elements (1, 2 and 3), but as you can see, they are in different orders.
You can see this property by running the code in the console below. Click the green arrow to see the output from this code.
<iframe frameborder="0" width="100%" height="400px" src="https://repl.it/@DSExperience/SetCompare?lite=true"></iframe>Python tells us that these sets are identical! With the set data type, the order is not important. Wow! What about lists, do they have these same properties as well? Let's see how a list acts in the same code.
Run the code console below to see if a list shares the same properties with a set.
We just learned that order matters for lists, but not sets! But let's take a step back: why does this matter to us? Remember, one of the steps in our plan was:
- Designate a spot for each unique word in our index cards
In our case, a set will create a collection of all of the individual words in the song, but as you've seen, the order will not remain. You'll first get the set of unique words and will then convert it to a list so that you can maintain the order integrity. As a first step, you'll create the set of unique words. This can be accomplished this with the following code:
unique_words = set(list_of_lyrics)
Click on the green arrow and type in unique_words to see what this set looks like.
You can see here that the list of unique words is significantly smaller than the total list of words. How much smaller? Let's run the codeblock below to find out.
<iframe frameborder="0" width="100%" height="700px" src="https://repl.it/@DSExperience/Setcompare?lite=true"></iframe>That's a lot!
So, there's a lot of repetition in Barbara Ann. It's time to keep track of each word and the number of occurrences of each word.
One of the goals is to present the list of repetitions almost as a table, with a (unique) word to the left and the number of occurrences to the right, this is known as a frequency table, you'll learn more about that in a later lesson. Below is an example of what a frequency table looks like:
| unique_words | count |
|---|---|
| Ann | 2 |
| Barbara | 3 |
| Ba | 8 |
Now that you have a collection with the unique words, you'll need to make sure the order of unique words is fixed, because you'll start matching a value to it (the value being equal to how often the word occurs in the song). So let's convert the unique_words set to a list. You can do this by using one simple line of code and the list() function. You can simply provide our set as an argument to the list() function like this:
unique_words = list(unique_words)
You can check that this worked by passing the variable name unique_words as an arguement to the type() function.
Run the cell below to see how this works.
<iframe frameborder="0" width="100%" height="500px" src="https://repl.it/@DSExperience/TypeFunction?lite=true"></iframe>In this lesson, you learned the difference between a list and a set. You also discovered that the order is not important in a set, but that a list will maintain the order of the data. You also learned about a function to check the type of data that is referenced by a variable as well as how to convert an unordered set back to an ordered list. Now that the data is in the desired format, let's move on and begin to count the occurrences of each word in our lyrics. We will learn how we can create a collection of so-called "key-value" pairs by using annother data type called a dictionary dict in the next section.