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Let's cover sets.

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They are also a type of collection.

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Sets are a type of collection.

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This means that like lists and tuples,

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you can input different Python types.

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Unlike lists and tuples, they are unordered.

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This means sets do not record element position.

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Sets only have unique elements.

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This means there is only one of a particular element in a set.

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To define a set, you use curly brackets.

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You place the elements of a set within the curly brackets.

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You notice there are duplicate items.

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When the actual set is created,

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duplicate items will not be present.

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You can convert a list to a set by using the function set,

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this is called type casting.

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You simply use the list as the input to the function set.

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The result will be a list converted to a set.

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Let's go over an example.

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We start off with a list.

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We input the list to the function set.

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The function set returns a set.

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Notice how there are no duplicate elements.

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Let's go over set operations.

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These could be used to change the set.

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Consider the set A.

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Let's represent this set with a circle.

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If you are familiar with sets,

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this could be part of a venn diagram.

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A venn diagram is a tool that uses shapes usually to represent sets.

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We can add an item to a set using the add-method.

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We just put the set name followed by a dot,

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then the add-method.

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The argument is the new element of the set we would like to add,

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in this case, NSYNC.

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The set A now has in NSYNC as an item.

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If we add the same item twice,

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nothing will happen as there can be no duplicates in a set.

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Let's say we would like to remove NSYNC from set A.

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We can also remove an item from a set using the remove-method.

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We just put the set name followed by a dot,

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then the remove-method.

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The argument is the element of the set we would like to remove,

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in this case, NSYNC.

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After the remove-method is applied to the set,

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set A does not contain the item NSYNC.

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You can use this method for any item in the set.

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We can verify if an element is in the set using the in command as follows.

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The command checks that the item,

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in this case AC/DC, is in the set.

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If the item is in the set, it returns true.

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If we look for an item that is not in the set,

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in this case for the item Who,

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adds the item is not in the set,

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we will get a false.

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These are types of mathematical set operations.

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There are other operations we can do.

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There are lots of useful mathematical operations we can do between sets.

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Let's define the set album set one.

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We can represent it using a red circle or venn diagram.

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Similarly, we can define the set album set two.

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We can also represent it using a blue circle or venn diagram.

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The intersection of two sets is

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a new set containing elements which are in both of those sets.

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It's helpful to use venn diagrams.

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The two circles that represent the sets combine,

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the overlap, represents the new set.

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As the overlap is comprised with the red circle and blue circle,

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we define the intersection in terms of and.

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In Python, we use an ampersand to find the intersection of the two sets.

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If we overlay the values of the set over

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the circle placing the common elements in the overlapping area,

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we see the correspondence.

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After applying the intersection operation,

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all the items that are not in both sets disappear.

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In Python, we simply just place the ampersand between the two sets.

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We see that both AC/DC and Back in Black are in both sets.

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The result is a new set album: set three

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containing all the elements in both albums set one and album set two.

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The union of two sets is the new set of

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elements which contain all the items in both sets.

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We can find the union of the sets album set one and album set two as follows.

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The result is a new set that has all the elements of album set one and album set two.

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This new set is represented in green.

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Consider the new album set-album set three.

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The set contains the elements AC/DC and Back in Black.

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We can represent this with a Venn diagram,

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as all the elements and album set three are in album set one.

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The circle representing album set one

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encapsulates the circle representing album set three.

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We can check if a set is a subset using the issubset method.

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As album set three is a subset of the album set one,

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the result is true.

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There is a lot more you can do with sets.

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Check out the lab for more examples.

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(Music)