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Split a list using another list whose items are the split lengths
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thewhosearesplititemsanotherusinglengthslist
Problem
I want to split a list using another list which contains the lengths of each split.
E.g:
As you can notice, if the lengths list does not cover all the list I append the remaining elements as an additional sublist. Also, I want to avoid empty lists at the end in the cases that the lengths list produces more elements that are in the list to split.
I already have a function that works as I want:
But I wonder if there is a more pythonic way to write a function such that one.
Note: I grabbed
Note: This question is a repost from a stackoverflow question
E.g:
>>> print list(split_by_lengths(list('abcdefg'), [2,1]))
... [['a', 'b'], ['c'], ['d', 'e', 'f', 'g']]
>>> print list(split_by_lengths(list('abcdefg'), [2,2]))
... [['a', 'b'], ['c', 'd'], ['e', 'f', 'g']]
>>> print list(split_by_lengths(list('abcdefg'), [2,2,6]))
... [['a', 'b'], ['c', 'd'], ['e', 'f', 'g']]
>>> print list(split_by_lengths(list('abcdefg'), [1,10]))
... [['a'], ['b', 'c', 'd', 'e', 'f', 'g']]
>>> print list(split_by_lengths(list('abcdefg'), [2,2,6,5]))
... [['a', 'b'], ['c', 'd'], ['e', 'f', 'g']]
As you can notice, if the lengths list does not cover all the list I append the remaining elements as an additional sublist. Also, I want to avoid empty lists at the end in the cases that the lengths list produces more elements that are in the list to split.
I already have a function that works as I want:
def take(n, iterable):
"Return first n items of the iterable as a list"
return list(islice(iterable, n))
def split_by_lengths(list_, lens):
li = iter(list_)
for l in lens:
elems = take(l,li)
if not elems:
break
yield elems
else:
remaining = list(li)
if remaining:
yield remaining
But I wonder if there is a more pythonic way to write a function such that one.
Note: I grabbed
take(n, iterable) from Itertools RecipesNote: This question is a repost from a stackoverflow question
Solution
This is my first answer that I gave on stackoverflow:
Here I am not using a for-else loop because we can end the generator by using a simple
Second answer:
This one is slightly different from the first one because this won't short-circuit as soon as one of the length exhausts the iterator. But it is more compact compared to my first answer.
from itertools import islice
def split_by_lengths(seq, num):
it = iter(seq)
for n in num:
out = list(islice(it, n))
if out:
yield out
else:
return #StopIteration
remain = list(it)
if remain:
yield remainHere I am not using a for-else loop because we can end the generator by using a simple
return statement. And IMO there's no need to define an extra take function just to slice an iterator.Second answer:
This one is slightly different from the first one because this won't short-circuit as soon as one of the length exhausts the iterator. But it is more compact compared to my first answer.
def split_by_lengths(seq, num):
it = iter(seq)
out = [x for x in (list(islice(it, n)) for n in num) if x]
remain = list(it)
return out if not remain else out + [remain]Code Snippets
from itertools import islice
def split_by_lengths(seq, num):
it = iter(seq)
for n in num:
out = list(islice(it, n))
if out:
yield out
else:
return #StopIteration
remain = list(it)
if remain:
yield remaindef split_by_lengths(seq, num):
it = iter(seq)
out = [x for x in (list(islice(it, n)) for n in num) if x]
remain = list(it)
return out if not remain else out + [remain]Context
StackExchange Code Review Q#46246, answer score: 5
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