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How to convert array of array into set in Python 3? [duplicate]

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What I have as input:

list: [[2, 4], [2, 6], [2, 8]]


What I want as output:

set: 2,4,6,8


What I'm currently doing(not working):

def convert(input_list):
all_nums = set([arr[0], arr[1]] for arr in input_list)
return all_nums


I know I can manually iterate through parent array and add contents of child array to the set like this:

set

def convert(input_list):
all_nums = set()
for inner_list in input_list:
all_nums.add(inner_list[0])
all_nums.add(inner_list[1])
return all_nums


all_nums.add(inner_list[0], inner_list[1])

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1, 2, 3, 4

5 Answers
5

Simply:

my_list = [[2, 4], [2, 6], [2, 8]]
my_set = e for l in my_list for e in l


This is using a "set comprehension", which is a squashed down version of:

my_list = [[2, 4], [2, 6], [2, 8]]
my_set = set()
for l in my_list:
for e in l:
my_set.add(e)


Alternatively, you could do:

my_list = [[2, 4], [2, 6], [2, 8]]
my_set = set()
for l in my_list:
my_set.update(l)


(Variable names shamelessly stolen from modesitt.)

my_set = (l[0], l[1]) for l in my_list

my_set = tuple(l) for l in my_list

my_set = (x, y) for x, y in my_list

all_nums.add((inner_list[0], inner_list[1]))

(2, 8), (2, 6), (2, 4)

One approach using itertools.chain and set

itertools.chain

set

Ex:

from itertools import chain
l = [[1, 2], [1, 3], [1, 4]]
print(set(chain.from_iterable(l)))


Output:

set([1, 2, 3, 4])


chain

You can try this:

from itertools import chain

l = [[1, 2], [1, 3], [1, 4]]
l = list(chain.from_iterable(l))
set_l = set(l)


I would do the following

set_ = e for l in my_list for e in l


x

y

e

l

You can use set comprehension:

l = [[2, 4], [2, 6], [2, 8]]
print(i for s in l for i in s)


This outputs:

8, 2, 4, 6