I have a list like this:
[[(video1,4)], [(video2,5),(video3,8)], [(video1,5)], [(video5, 7), (video6,9)]...]
each item in this list may contain a single data pair, or a tuple, I want to change this list into
[(video1,4),(video2,5),(video3,8),(video1,5),(video5,7),(video6,9)...]
then do this:
for item in list:
reqs = reqs + item[1]
b.append(item[0])
c = set(b)
I don't know how to change the list structure, or how to do the same calculation based on the original list?
如果您只想展平列表,只需使用itertools.chain.from_iterable
: http : //docs.python.org/library/itertools.html#itertools.chain.from_iterable
There is a very simple way of doing this with list comprehensions. This example has been documented in the python documentation here
>>> # flatten a list using a listcomp with two 'for'
>>> vec = [[1,2,3], [4,5,6], [7,8,9]]
>>> [num for elem in vec for num in elem]
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Here is the solution that you would want to implement. As per your example, this is the simplest solution
In [59]: your_list = [[('video1',4)], [('video2',5),('video3',8)], [('video1',5)], [('video5', 7), ('video6',9)]]
In [60]: improved_list = [num for elem in your_list for num in elem]
In [61]: improved_list
Out[61]:
[('video1', 4),
('video2', 5),
('video3', 8),
('video1', 5),
('video5', 7),
('video6', 9)]
要展平一个级别,可以使用itertools.chain.from_iterable()
:
flattened_list = itertools.chain.from_iterable(my_list)
Here's another one (no libraries):
def plus(a,b): return a + b
reduce(plus, your_list)
Try this:
from itertools import chain
c = set()
reqs = 0
for vid, number in chain(*your_list):
c.add(vid)
reqs += number
Also see related post Flattening a shallow list in Python .
There should be negligible performance increase from using chain.from_iterable(list)
rather than chain(*list)
, but it's true that the former looks cleaner.
If this list is singly-nested (list of lists) you can do this, which I use a lot :
flat_list = sum(list_of_lists, [])
This works due to the fact that sum simply adds up the lists, and adding up lists works in python as expected :)
Note : This is inefficient and some say unreadable.
to extract all tuples from a data structure ...
def get_tups(y):
z = []
if y:
for x in y:
if isinstance(x, tuple):
z.append(x)
else:
z.extend(get_tups(x))
return z
maybe ...
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