Infinite Loop and Rotation of Array

Question

so I have this list,

List: [0, 0, 1, 0, 1];

And I need made a algorithm with a for to show all the list (list[i]).

When I am in first array position, I can do list[i-2] and list[i-1], with this I can see the elements of the last position and the position before the last position.

Exemple : list[0] = 0; list[i-1] = list[4] = 1; list[i-2] = list[3] = 0; so I can go to the last position and start from there.

But when I do, list[i+1] in the last position I got a IndexError: list index out of range from the terminal.

My question is: If I was in the last positions and I want again come to from the first one and keep doing the for loop, to see infinite times all array elements from all positions, How I can do it? If the size of my array it is 5, and I am in second position(list[1]) in the loop and want do list[i + 11], how can I put this representing this, list[2]?

I am trying make this on python.

Ha, missed the lookup part. They should be using the wrapping with modulo then. But they can throw in `islice` with `cycle` if they want — Moses Koledoye, Apr 01 '17 at 22:50
@MosesKoledoye this dont come to the begining of array again :s it is just a internal array funcionalaties. — Miguel Soeiro, Apr 01 '17 at 22:53
I have no idea what you're trying to ask, and it looks like no one else has a clear idea either. — TigerhawkT3, Apr 01 '17 at 22:57
@TigerhawkT3 Imagine a loop to show all element of the array, the size of array is 7 and I want make a loop 10 times, so when it is on last position (on list[6]) they need to come to the begining again and show 3 elements from there. — Miguel Soeiro, Apr 01 '17 at 23:01
That would be a cycle. See the linked question and its answers. — TigerhawkT3, Apr 01 '17 at 23:03
@TigerhawkT3 yes but if I have a array like [1,2,3,4,5,6], and want start from one time in second, and next start from last position, I can do it with this itertools.cycle — Miguel Soeiro, Apr 01 '17 at 23:15
I am glad to hear that you can do it with the methods in the provided link. — TigerhawkT3, Apr 01 '17 at 23:16

score 1 · Answer 1 · answered Apr 01 '17 at 22:49

You can achieve this using the modulo operator, which returns the remainder of the division of its two operands. In this case, you would do the following: list[i%num_of_elements], where num_of_elements is a variable holding the number of elements in the list.

score 1 · Answer 2 · answered Apr 01 '17 at 22:54

1

I believe your asking about rotating arrays, if this isn't what you meant, just comment.

def rotateLeft(li):
    return li[1:] + [li[0]]

def rotateRight(li):
    return [li[len(li)-1]] + li[:len(li)-1]

li = [1,2,3,4,5]

print (rotateLeft(li))
print (rotateRight(li))

answered Apr 01 '17 at 22:54

Neil

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`rotateRight(li)` can be simplified like `return [li[-1]] + li[:-1]` – Johan Aug 31 '18 at 20:44
Or, perhaps more efficient version of `rotateLeft()` would be `li.append(li.pop(0))` (though I don't know how it works internally in python). – Johan Aug 31 '18 at 20:47

score 0 · Accepted Answer · answered Apr 01 '17 at 22:59

0

You can implement such an "infinite iterator" as follows:

def infinite_iterator(lst):    
    i = 0
    def next():        
        global i
        while True:
            result = lst[i % len(lst)]
            i += 1
            yield result
    return next()

and use it with:

lst = [1,2,3,4,5]    
iter = infinite_iterator(lst)

for i in range(17): # 17 is just an example, you can put any number or `while True:` 
    print(next(iter))

answered Apr 01 '17 at 22:59

Nir Alfasi

53,191
11
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1

Thank you man! Its exactly what I am trying find. Thanks! – Miguel Soeiro Apr 01 '17 at 23:09

Infinite Loop and Rotation of Array

3 Answers3