Python Equivalent to Ruby's #each_cons?
I don't think there is one, I looked through the built-in module itertools
, which is where I would expect it to be. You can simply create one though:
def each_cons(x, size):
return [x[i:i+size] for i in range(len(x)-size+1)]
For such things, itertools
is the module you should be looking at:
from itertools import tee, izip
def pairwise(iterable):
"s -> (s0,s1), (s1,s2), (s2, s3), ..."
a, b = tee(iterable)
next(b, None)
return izip(a, b)
Then:
>>> list(pairwise([1, 2, 3, 4]))
[(1, 2), (2, 3), (3, 4)]
For an even more general solution, consider this:
def split_subsequences(iterable, length=2, overlap=0):
it = iter(iterable)
results = list(itertools.islice(it, length))
while len(results) == length:
yield results
results = results[length - overlap:]
results.extend(itertools.islice(it, length - overlap))
if results:
yield results
This allows arbitrary lengths of subsequences and arbitrary overlapping. Usage:
>> list(split_subsequences([1, 2, 3, 4], length=2))
[[1, 2], [3, 4]]
>> list(split_subsequences([1, 2, 3, 4], length=2, overlap=1))
[[1, 2], [2, 3], [3, 4], [4]]
My solution for lists (Python2):
import itertools
def each_cons(xs, n):
return itertools.izip(*(xs[i:] for i in xrange(n)))
Edit: With Python 3 itertools.izip
is no longer, so you use plain zip
:
def each_cons(xs, n):
return zip(*(xs[i:] for i in range(n)))