I'm using Python to infinitely iterate over a list, repeating each element in the list a number of times. For example given the list:
l = [1, 2, 3, 4]
I would like to output each element two times and then repeat the cycle:
1, 1, 2, 2, 3, 3, 4, 4, 1, 1, 2, 2 ...
I've got an idea of where to start:
def cycle(iterable):
if not hasattr(cycle, 'state'):
cycle.state = itertools.cycle(iterable)
return cycle.next()
>>> l = [1, 2, 3, 4]
>>> cycle(l)
1
>>> cycle(l)
2
>>> cycle(l)
3
>>> cycle(l)
4
>>> cycle(l)
1
But how would I repeat each element?
Edit
To clarify this should iterate infinitely. Also I've used repeating the element twice as the shortest example - I would really like to repeat each element n times.
Update
Will your solution lead me to what I was looking for:
>>> import itertools
>>> def ncycle(iterable, n):
... for item in itertools.cycle(iterable):
... for i in range(n):
... yield item
>>> a = ncycle([1,2], 2)
>>> a.next()
1
>>> a.next()
1
>>> a.next()
2
>>> a.next()
2
>>> a.next()
1
>>> a.next()
1
>>> a.next()
2
>>> a.next()
2
Thanks for the quick answers!
The * operator can also be used to repeat elements of a list. When we multiply a list with any number using the * operator, it repeats the elements of the given list. Here, we just have to keep in mind that to repeat the elements n times, we will have to multiply the list by (n+1).
You can loop through the list items by using a while loop. Use the len() function to determine the length of the list, then start at 0 and loop your way through the list items by referring to their indexes. Remember to increase the index by 1 after each iteration.
How about this:
import itertools
def bicycle(iterable, repeat=1):
for item in itertools.cycle(iterable):
for _ in xrange(repeat):
yield item
c = bicycle([1,2,3,4], 2)
print [c.next() for _ in xrange(10)]
EDIT: incorporated bishanty's repeat count parameter and Adam Rosenfield's list comprehension.
You could do it with a generator pretty easily:
def cycle(iterable):
while True:
for item in iterable:
yield item
yield item
x=[1,2,3]
c=cycle(x)
print [c.next() for i in range(10)] // prints out [1,1,2,2,3,3,1,1,2,2]
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