Suppose I have a set {a, b, c, d}. I want to create a "path" from it, which is a generator that yields (a, b), then (b, c), then (c, d) (of course set is unordered, so any other path through the elements is acceptable).
What is the best way to do this?
def gen(seq):
it = iter(seq)
a, b = next(it), next(it)
while True:
yield (a, b)
a, b = b, next(it)
print(list(gen({1, 2, 3, 4})))
Here's an example using the pairwise() recipe from http://docs.python.org/3/library/itertools.html#itertools-recipes
>>> from itertools import tee
>>> def pairwise(iterable):
... "s -> (s0,s1), (s1,s2), (s2, s3), ..."
... a, b = tee(iterable)
... next(b, None)
... return zip(a, b)
...
>>> for pair in pairwise({1, 2, 3, 4}):
... print(pair)
...
(1, 2)
(2, 3)
(3, 4)
Use the Rolling or sliding window iterator in Python solution:
>>> from itertools import islice
>>> def window(seq, n=2):
... "Returns a sliding window (of width n) over data from the iterable"
... " s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ... "
... it = iter(seq)
... result = tuple(islice(it, n))
... if len(result) == n:
... yield result
... for elem in it:
... result = result[1:] + (elem,)
... yield result
...
>>> path = window({1, 2, 3, 4})
>>> for step in gen:
... print path
(1, 2)
(2, 3)
(3, 4)
This happens to follow sorted order, because for python integers hash(x) == x and thus the sequence of 1, 2, 3, 4 is inserted in that order into the set.
You could use the pairwise itertools recipe:
>>> from itertools import tee
>>> def pairwise(iterable):
a, b = tee(iterable)
next(b, None)
return zip(a, b)
>>> pairwise({1, 2, 3, 4})
<zip object at 0x0000000003B34D88>
>>> list(_)
[(1, 2), (2, 3), (3, 4)]
Now that I understand the question
from itertools import islice
a = {'A','B','C','D'}
zip(a,islice(a,1,None))
#[('A', 'C'), ('C', 'B'), ('B', 'D')]
