With below dictionary, I want to make a new single list with all directories:

nominated = {1931: ['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg'],
             1932: ['Frank Borzage', 'King Vidor', 'Josef Von Sternberg'],
             1933: ['Frank Lloyd', 'Frank Capra', 'George Cukor']}

Desired output: 1 single list with all directors

all_directors = ['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg','Frank Borzage', 'King Vidor', 'Josef Von Sternberg','Frank Lloyd', 'Frank Capra', 'George Cukor']

Attempt 1: list comprehension

all_directors = [[director for director in nominated_directors] for year, nominated_directors in nominated.items()]

print(all_directors)

Output attempt 1

[['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg'], ['Frank Borzage', 'King Vidor', 'Josef Von Sternberg'], ['Frank Lloyd', 'Frank Capra', 'George Cukor']]

Attempt 1: using for loop

all_directors = []
for year, directors in nominated.items():
    for director in directors:
        all_directors.append(director)

print(all_directors)

Output attempt 2

['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg', 'Frank Borzage', 'King Vidor', 'Josef Von Sternberg', 'Frank Lloyd', 'Frank Capra', 'George Cukor']

The output is correct with for loop but not list comprehension. Not sure what I missed, can you please help?

CodePudding user response：

all_directors = [
    director for year, nominated_directors in nominated.items() 
    for director in nominated_directors
    ]

You can just remove the list notation from attempt 1 and re-order the for loops in list comprehension.

CodePudding user response：

The problem you have here is the order you are iterating over items.

Your for loop correctly iterates over the major items (the sub lists of director names), then within that looping loops over the minor items (the actual names).

For some reason you've reversed this in your attempt at a list comprehension!

Sorting this out we have..

nominated = {1931: ['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg'],
             1932: ['Frank Borzage', 'King Vidor', 'Josef Von Sternberg'],
             1933: ['Frank Lloyd', 'Frank Capra', 'George Cukor']}

all_directors  = [name for year,director_sublist in nominated.items() for name in director_sublist]

print(all_directors)


['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg', 'Frank Borzage', 'King Vidor', 'Josef Von Sternberg', 'Frank Lloyd', 'Frank Capra', 'George Cukor']

Incidentally we don't care about the dictionary keys (the years), so can dispense with them and just iterate over the dictionary values (the lists of director names)..

all_directors  = [name for director_sublist in nominated.values() for name in director_sublist]

Finally, why not make this a set rather than a list comprehension? Get rid of the duplicated names just by replacing [...] with {...}

nominated = {1931: ['Norman Taurog', 'Wesley Ruggles', 'Clarence Brown', 'Lewis Milestone', 'Josef Von Sternberg'],
             1932: ['Frank Borzage', 'King Vidor', 'Josef Von Sternberg'],
             1933: ['Frank Lloyd', 'Frank Capra', 'George Cukor']}

all_directors  = {name for director_sublist in nominated.values() for name in director_sublist}

print(all_directors)

{'Frank Lloyd', 'Frank Capra', 'King Vidor', 'Josef Von Sternberg', 'Wesley Ruggles', 'Norman Taurog', 'Lewis Milestone', 'Frank Borzage', 'Clarence Brown', 'George Cukor'}

CodePudding user response：

You can use sum to flatten the result.

all_directors = sum([[director for director in nominated_directors] for year,
                     nominated_directors in nominated.items()],
                    [])

You can also slim it down using map:

all_directors = sum(list(map(list, nominated.values())), [])

Or even further (thanks to Kelly Bundy in the comments) with:

sum(nominated.values(), [])

CodePudding user response：

you can use this nested loop in list comperhension to get all directories into single list

all_directors =[director for year, directors in nominated.items() for director in directors] print(all_directors)

CodePudding user response：

You problem is a nested list comprehension case. Below is the solution.

all_directors = [director for nominated_directors in nominated.values() for director in nominated_directors]