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You have completed Python Sets!
You have completed Python Sets!
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There are four main set operations that allow you to compare and contrast collections like a Venn Diagram. Union and Intersection are two methods for comparing shared membership between sets.
Main Set Operations
The following methods and operations return a new set.
s.intersection(t) / s & t - Return the intersection of two sets as a new set. (i.e. all elements that are in both sets.)
s.union(t) / s | t - Return the union of sets as a new set. (i.e. all elements that are in either set.)
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In our last video,
we used Euler diagrams to illustrate
0:00
the relationship between a subset and
a superset.
0:04
A set can be a subset of another set when
all of its members are found in another.
0:08
What happens when some, but not all of
the members of one set are in another?
0:15
We can illustrate these
relationships with a Venn diagram.
0:21
Remember that we can use
a Venn diagram to compare and
0:26
contrast the memberships of sets.
0:30
The common members go where
the circles overlap, and
0:33
unique members stay on the sides.
0:38
Each section of the Venn diagram
is a set with a specific name
0:41
that describes a subset or
superset relationship.
0:46
Let's use real-world examples to learn
about these special Venn diagrams sets and
0:50
what they are called.
0:56
I used to work in restaurants, and
0:57
my favorite time to work
was the breakfast service.
1:00
Let's imagine comparing two omelets.
1:03
We can represent the ingredients of
each omelet as members of a set.
1:06
The entire diagram can be thought of
as a superset, we call that the union.
1:11
Union is a set of all of
the members of both sets.
1:17
Intersection is a subset of all of
the members common to both sets.
1:22
It is where the Venn diagram overlaps.
1:28
This can be an empty set.
1:31
Difference is a subset of the members
unique to one set, but not the other.
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In Python, it will be the leftmost set.
1:39
Symmetric difference is a subset
of the members unique to each set.
1:43
So members of the left and
right sides but not the middle.
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It's equivalent to the union
minus the intersection.
1:52
Now let's try it out in Python.
1:58
Our restaurant has been doing well and
we now have five omelets on our menu.
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Just like in a real restaurant's menu, the
ingredients are in no particular order.
2:06
We need to learn about
the similarities and
2:11
differences between the omelets we serve.
2:14
First, I need to know about all
of the ingredients to stock so
2:16
that my kitchen doesn't run out of food.
2:20
We can take the union of our five sets
to get a set of all the ingredients that
2:23
I need in my kitchen.
2:27
There are three ways to do this.
2:28
And we'll start small,
first with the union of two omelets.
2:31
I'll take the union of the turkey and
vegetarian omelets first.
2:38
turkey.union(vegetarian).
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And we'll print this out to the terminal.
2:48
We get back a set of all the ingredients
with the duplicates removed.
2:56
And we can chain the method call with more
dot notation to get the union of more
3:00
than two omelets.
3:05
Here, I'll add in a .union, and
I'll take the union of turkey,
3:08
vegetarian, and the denver omelets.
3:14
Chaining method calls together with
dot notation can become very verbose.
3:20
You can imagine how far this
line of code on line 12 will
3:25
stretch if I pass in all five
omelets in the same manner.
3:29
Luckily for us, the union method can
also take more than one argument
3:34
All I have to do is separate
them by commas, and
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when I print in my terminal,
I get the exact same thing,
3:45
a set of all the ingredients
with the duplicates removed.
3:49
For five sets, this process
can still become very verbose.
3:54
So we can also use a shorthand
operator for union,
3:58
which is the vertical pipe symbol.
4:01
On the keyboard, that's between
the Backspace and Return keys or
4:04
Shift and Backslash.
4:09
We're making a new set.
4:11
So first, I'll declare a new variable,
all_ingredients.
4:12
And assign it to the union
of all five omelets,
4:18
turkey | denver | vegetarian
| bacon | smothered.
4:24
And I'll print this out to the terminal.
4:32
There we have it.
4:48
A nice and concise way of printing
out all of the ingredients
4:49
with none of the duplicates.
4:54
This is the union.
4:56
Great, next I need to
know what ingredients
4:59
are common to all five omelets.
5:03
They will be the most important,
5:06
because if I run out of any of these
ingredients, I can't make any more food.
5:08
In other words,
5:13
I need to find the intersection of all
of the ingredients of all five omelets.
5:14
The intersection is the middle
overlapping part of the Venn diagram.
5:20
Let's start with two, the vegetarian and
bacon omelets this time.
5:26
vegetarian.intersection(bacon).
5:32
We'll print this out in our terminal.
5:40
The ingredients in common
of the vegetarian and
5:50
bacon omelets are onion, cheese,
eggs, mushroom and avocado.
5:53
And for five, we can use the shorthand
operator, which is the ampersand symbol.
5:58
shared_ingredients =
6:06
vegetarian & bacon &
6:12
denver & mothered & turkey.
6:17
print(shared_ingredients)
6:28
Eggs, onion, and
cheese are the common ingredients
6:41
shared between all five of my omelette.
6:45
So in my restaurant, I'll make sure to
stock up extra of eggs, onion, and cheese.
6:49
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