CODEWITHSUNDEEP
pythonlist
user10634518
user10634518

Reputation:

get keys and values from a Python dictionary as lists

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,

Upvotes: 2

Views: 721

Answers (3)

hiro protagonist
hiro protagonist

Reputation: 46899

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))

Upvotes: 1

deceze
deceze

Reputation: 522402

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)).

Upvotes: 2

Mayank Porwal
Mayank Porwal

Reputation: 34086

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]

Upvotes: 0

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