I have the following output from a code I ran on Python:
T1 = [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]
I want to extract the keys and values from each object respectively. For T1, I would thus have:
P1 = [0,15,19,20,0]
D1 = [0, 3, 1,1,0]
What would be the best way to code it?
Thanks in advance,
Sounds like a good case for chain.from_iterable:
>>> from itertools import chain
>>> from operator import methodcaller
>>> T1 = [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]
>>> list(chain.from_iterable(T1))
[0, 15, 19, 20, 0]
>>> list(chain.from_iterable(map(methodcaller('values'), T1)))
[0, 3, 1, 1, 0]
A dictionary when iterated over yields its keys; chain.from_iterable takes a list of such iterables and yields all their keys in a sequence. To do the same with the values, call values() on each item, for which we map a methodcaller here (equivalent to (i.values() for i in T1)).
this should work:
T1 = [{0: 0}, {15: 3}, {19: 1}, {20: 1}, {0: 0}]
P1 = [next(iter(dct)) for dct in T1]
D1 = [next(iter(dct.values())) for dct in T1]
you take the first element (next) of an iterator over the keys (iter(dct)) or an interator over the values (iter(dct.values()).
this will not create any unnecessary lists.
or in one go (note: these return tuples not lists):
P1, D1 = zip(*(next(iter(dct.items())) for dct in T1))
or (using parts of deceze's answer):
from itertools import chain
P1, D1 = zip(*chain.from_iterable(dct.items() for dct in T1))
[] → ()) for even more efficiency in that zip approach.
Use List Comprehensions:
In [148]: P1 = [list(i.keys())[0] for i in T1]
In [149]: D1 = [list(i.values())[0] for i in T1]
In [150]: P1
Out[150]: [0, 15, 19, 20, 0]
In [151]: D1
Out[151]: [0, 3, 1, 1, 0]