I have a list (e.g. a = [1, 2, 3, [1, 2, 4]]) and I want to create a set from its elements at the lowest levels of the nesting (in the previous example, to obtain setA = {1, 2, 3, 4}).
Running set(a) gives me the error:
TypeError: unhashable type: 'list'
What should I do to obtain such a set?
You will have to first flatten the irregularly nested list. Below are 2 solutions that will handle any depth, irregularly nested lists.
Try collections for flattening the irregular deep nested list -
import collections
def flatten(x):
if isinstance(x, collections.Iterable):
return [a for i in x for a in flatten(i)]
else:
return [x]
a = [1, 2, 3, [1, [2, 4]]] #Irregular deep nested list
out = set(flatten(a))
out
{1, 2, 3, 4}
More details here.
For lists that are nested deeper, you can use recursion -
def flatten(S):
if S == []:
return S
if isinstance(S[0], list):
return flatten(S[0]) + flatten(S[1:])
return S[:1] + flatten(S[1:])
a = [1, 2, 3, [1, [2, 4]]] #Irregular deep nested list
out = set(flatten(a))
out
{1, 2, 3, 4}
More details here.
If like me, you prefer using one-liners, try this lambda function with recursion -
f = lambda *n: (e for a in n for e in (f(*a) if isinstance(a, (tuple, list)) else (a,)))
out = set(f(a))
out
{1, 2, 3, 4}
More details here.
Here is my suggestion. It uses recursion and works with any level of nested structure:
import collections
def getset(l):
res=set()
for i in l:
if isinstance(i, collections.Iterable):
res=res.union(getset(i))
else:
res.add(i)
return res
getset(a)
#{1,2,3,4}
getset([1, 2, 3, [4, 5, [10, 20, [100, 200]]], [12, 14, [16, 18]]])
#{1, 2, 3, 4, 5, 100, 200, 10, 12, 14, 16, 18, 20}
