I have array [1,2,1,2,3,4,3,4,1,2]
I want to loop it x times, each times moving array every element 1 position forward:
So next loop will be:
2.[2,1,2,3,4,3,4,1,2,1]
3.
[1,2,3,4,3,4,1,2,1,2]
etc....
How can I manipulate array like this way?
EDIT:
What I thought, but maybe some better tricks:
Just go over the array with while loop and create new array with for cycle.
for i in range(11)
array[i] = array[i-1]
etc etc..its pseudo code
Using a List data structure isn't an efficient way to do this. A Queue would be more appropriate. In any case:
Using a Queue
As I suggested, using a Queue (collections.deque):
>>> q = collections.deque([1,2,3,4,5,6,7,8])
>>> for _ in xrange(5):
... q.rotate(-1)
...
>>> q
deque([6, 7, 8, 1, 2, 3, 4, 5])
Keeping the List
>>> a = [1,2,3,4,5,6,7,8]
>>> for _ in xrange(5):
... a = a[1:] + a[:1]
...
>>> a
[6, 7, 8, 1, 2, 3, 4, 5]
Alternatively (faster than the previous one):
>>> a = [1,2,3,4,5,6,7,8]
>>> for _ in xrange(5):
... a.append(a.pop(0))
...
>>> a
[6, 7, 8, 1, 2, 3, 4, 5]
Here you can change xrange for whatever you want to iterate over.
Timeit analysis:
Pop-Append
>>> timeit.timeit('a.append(a.pop(0))', setup='a = [0,1,2,3,4,5,6,7,8,9]', number=1000000)
0.24548697471618652
>>> timeit.timeit('a.append(a.pop(0))', setup='a = [0,1,2,3,4,5,6,7,8,9]', number=100000000)
23.65538215637207
Slicing
>>> timeit.timeit('a=a[1:] + a[:1]', setup='a = [0,1,2,3,4,5,6,7,8,9]', number=1000000)
0.36037278175354004
>>> timeit.timeit('a=a[1:] + a[:1]', setup='a = [0,1,2,3,4,5,6,7,8,9]', number=100000000)
35.06173801422119
Queue
>>> timeit.timeit('q.rotate(-1)', setup='import collections; q = collections.deque([0,1,2,3,4,5,6,7,8])', number=1000000)
0.16829514503479004
>>> timeit.timeit('q.rotate(-1)', setup='import collections; q = collections.deque([0,1,2,3,4,5,6,7,8])', number=100000000)
16.012277841567993
With a little optimization, basically removing the __getattr__ call for append, pop and rotate:
Pop-Append
>>> timeit.timeit('aa(ap(0))', setup='a = [0,1,2,3,4,5,6,7,8,9]; aa=a.append; ap=a.pop', number=1000000)
0.15255093574523926
>>> timeit.timeit('aa(ap(0))', setup='a = [0,1,2,3,4,5,6,7,8,9]; aa=a.append; ap=a.pop', number=100000000)
14.50795292854309
Queue
>>> timeit.timeit('r(-1)', setup='import collections; q = collections.deque([0,1,2,3,4,5,6,7,8]); r=q.rotate', number=1000000)
0.13374090194702148
>>> timeit.timeit('r(-1)', setup='import collections; q = collections.deque([0,1,2,3,4,5,6,7,8]); r=q.rotate', number=100000000)
11.435136079788208
my_list = [1,2,1,2,3,4,3,4,1,2]
for i in range(10):
my_list.insert(0,my_list.pop())
print my_list
You question finds its answer in this question (which answers help in improving ...) Efficient way to shift a list in python
To make it short, make a function to shift your array:
def shift(l, n):
return l[n:] + l[:n]
Then call this function in a loop:
myarray=[1,2,3,4,5,6,7]
for ii in range(10):
myarray=shift(myarray, 1)
print myarray
