set

# set 요소 추가, 삭제 

nums1 = set()

nums2 = set()

nums1.add(1)

nums2.add(2)

 

nums1.update(nums2)

 

nums1.update([3])

nums1.update({4})

nums1.update('4')

print(nums1)

nums1.remove('4')

print(nums1)

 

 

# 결과

{1, 2, 3, 4, '4'}

{1, 2, 3, 4}

 

 

# set - operators

a, b = set(), set()

a = {1, 2}

b = {1, 3}

 

print(a - b)

print(a.difference(b))

 

print(a ^ b)

print(a.symmetric_difference(b))

 

print(a & b)

print(a.intersection(b))

 

x, y = set(), set()

x = {'aa', 'bb'}

y = {'aa', 'cc'}

 

print(x.difference('bb'))

print(x.difference({'bb'}))

 

# 결과

{2}

{2}

{2, 3}

{2, 3}

{1}

{1}

{'aa', 'bb'}

{'aa'}

 

# A set is a data type that consists of a collection of items
# much like a list.
# However, sets differ from lists in two important ways.
# The first is that they cannot have duplicate values in them,
# and the second is that the items they contain are unordered,
# like the key value pairs of a dictionary.

# Unlike lists or tuples sets cannot have their items accessed
# from them by index.
# So if you want to access the elements from a set,
# you can use a for loop.

# Sets are useful in situation where you want to use a collection
# of items, but you don't want duplicate items in the collection.

duplicate_nums = [1, 2, 3, 4, 1, 2, 3, 4, 5, 7, 10, 12, 10]
print(set(duplicate_nums))
print(f'length of duplicate_nums: {len(duplicate_nums)}')
print(list(set(duplicate_nums)))
print(f'length of unique nums: {len(list(set(duplicate_nums)))}')

# 결과
{1, 2, 3, 4, 5, 7, 10, 12}
length of duplicate_nums: 13
[1, 2, 3, 4, 5, 7, 10, 12]
length of unique nums: 8

 

# set의 복사
mountains = {'Everest', 'Kilimanjaro', 'Baekdoo'}
mountains2 = mountains.copy()
print(f'mountains is equal to mountains2? {mountains2 is mountains}')

# 결과
mountains is equal to mountains2? False

 

# set comprehensions

set_evens = {e for e in range(1, 10) if e % 2 == 0}
print(sorted(set_evens))

set_unique_letter = {l.lower() for l in 'ALLCAPS'}
print(sorted(set_unique_letter))

# 결과
[2, 4, 6, 8]
['a', 'c', 'l', 'p', 's']