How do i take multiple arbitrary values from different index positions in an iterator?
How to get the n next values of a generator in a list (python) and Get the nth item of a generator in Python describe the use of
itertools.islice for taking arbitrary element or continuous subset from an iterator. But what if i want multiple arbitrary elements from different positions in the iterator, where you can't just use
islice's step argument?
I'm trying to solve Project Euler's problem 40. I generated a string of concatenated integers with
iteration = (i for i in ''.join(map(str, (i for i in xrange(1,10**6)))))
An now i want to get elements with indexes 1, 10, 100, 1000, 10000, 100000, 1000000 counting from 1. I couldn't use
islice here, because every call to
next shifts current value to yield to the right. For example
next(islice(iteration, 1, 2)) + next(islice(iteration, 3, 4))
produces '26' instead of '24'.
Update (25.11.12, 4:43 UTC+0):
Thanks for all the suggestions. My current code looks like:
it = (i for i in ''.join(map(str, (i for i in xrange(1,10**6))))) ds = [int(nth(it, 10**i-10**(i-1)-1)) for i in range(7)] return product(ds)
The ugly argument for
nth is to generate a sequence of 0, 8, 89, 899, 8999 etc.