Using a set in python
problem
SOLUTION
Python comes with a built-in Set data structure. In order to use it we need to initialize,
for example in a local variable:
colors = set(['blue', 'green', 'red', 'gray']) # convert from list
The code above creates a set with 4 colors. The values are sourced from a list.
fruits = set(('apple', 'kiwi', 'pineapple')) # convert from tuple
This case we created a set from a tuple.
The set() can take an iterable collection and convert it to a set, for example a list or tuple.
If we have a list with duplicates and convert it to a set, the duplicates are dropped.
For example:
duplicates = ['sky','beach','building','sky','beach']
items = set(duplicates)
print(items)
output
As you can see the duplicated values have been discarded.
We can insert a new item using add()
colors.add('yellow')
print(colors)
output
It’s adding it at the end of the set.
Using pop(), for example:
colors = set(['blue', 'green', 'red', 'gray'])
first_color = colors.pop()
print(first_color) # gray
It will remove the last item from the set. In this case “gray”. The set now contains the following values.
output
We can do that by using remove(), we need to provide the item we wish to remove. For example, to remove “blue”
colors.remove(“blue”) #it will search for it and if found will remove it
If it’s not found, it will throw a KeyError.
Note: remove() does not return the item, pop() does.
The same like the remove() above, just it doesn’t throw an error in case the item is not in the set.
colors.clear()
This clears all the contents of the set.
Let’s say I want to create one set that is made of colors and fruits sets above.
colors = set(['blue', 'green', 'red', 'gray']) # create a set from a list
fruits = set(('apple', 'kiwi', 'pineapple')) # create a set from a tuple
new_set = colors.union(fruits) # merge the two sets into one
print(new_set)
output
To find the common items between two sets, we can use intersection()
nums = set([1,2,3,4,5,6,7,8,9,10])
even = set([0,2,4,6,8,10])
common = nums.intersection(even)
print(common)
output
nums = set([1,2,3,4,5,6,7,8,9,10])
even = set([0,2,4,6,8,10])
difference = nums.difference(even)
print(difference)
output
It returns the opposite of intersection, how two sets differ.
You can check if a set is a subset of another by using the issubset() function. For example:
odds = set([1,3,5])
nums =set ([1,2,3,4,5,6,7,8,9,10])
is_subset = odds.issubset(nums)
print(is_subset)
output
conclusion
In this post we saw how to initialize a Set from a list and from a tuple. A set contains only unique values by definition. Also, a set has ready functions on it that can be very useful for example finding the union, intersection, difference between two sets.
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Ellion
Professional IT consultant, writer, programmer enthusiast interested in all sorts of coding.
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