I have a data structure which looks like this:
{'A': [2, 3, 5, 6], 'B': [1, 2, 4, 7], 'C': [1, 3, 4, 5, 7], 'D': [1, 4, 5, 6], 'E': [3, 4]}
Using Python, I need to extract this:
{1, 2, 3, 4, 5, 6, 7}
Because I need a count of the distinct values for a mathematical equation further downstream.
Here is my current implementation, which works (complete code example):
from itertools import chain
# Create som mock data for testing
dictionary_with_lists = {'A': [2, 3, 5, 6],
'B': [1, 2, 4, 7],
'C': [1, 3, 4, 5, 7],
'D': [1, 4, 5, 6],
'E': [3, 4]}
print(dictionary_with_lists)
# Output: 'A': [2, 3, 5, 6], 'B': [1, 2, 4, 7], 'C': [1, 3, 4, 5, 7], 'D': [1, 4, 5, 6], 'E': [3, 4]}
# Flatten dictionary to list of lists, discarding the keys
list_of_lists = [dictionary_with_lists[i] for i in dictionary_with_lists]
print(f'list_of_lists: {list_of_lists}')
# Output: list_of_lists: [[2, 3, 5, 6], [1, 2, 4, 7], [1, 3, 4, 5, 7], [1, 4, 5, 6], [3, 4]]
# Use itertools to flatten the list
flat_list = list(chain.from_iterable(list_of_lists))
print(f'flat_list: {flat_list}')
# Output: flat_list: [2, 3, 5, 6, 1, 2, 4, 7, 1, 3, 4, 5, 7, 1, 4, 5, 6, 3, 4]
# Convert list to set to get only unique values
set_of_unique_items = set(flat_list)
print(f'set_of_unique_items: {set_of_unique_items}')
# Output: set_of_unique_items: {1, 2, 3, 4, 5, 6, 7}
While this works, but I suspect there might be a simpler and more efficient approach.
What would be a more efficient implementation which does not diminish code readability?
My real-world dictionary contains hundreds of thousands or millions of lists of arbitrary lengths.
Try this
from itertools import chain
d = {'A': [2, 3, 5, 6], 'B': [1, 2, 4, 7], 'C': [1, 3, 4, 5, 7], 'D': [1, 4, 5, 6], 'E': [3, 4]}
print(set(chain.from_iterable(d.values())))
Output:
{1, 2, 3, 4, 5, 6, 7}