I need to visit items in array starting to index random.
My code
from random import randrange
fruits = ['banana', 'apple', 'mango']
index = randrange(len(fruits))
for index in fruits[index:]:
print index
It is possible when index is 1 or 2 after to print start again in index 0 or 1 in that loop for.
Example:
Randon index is 1 print = 'apple' 'mango' 'banana'
Randon index is 2 print = 'mango' 'apple' 'banana'
Try this
from random import randrange
fruits = ['banana', 'apple', 'mango']
randomOffset = randrange(0,len(fruits))
for i in range(len(fruits)):
print fruits[i - randomOffset]
You could use an index of (i + randomOffset) % len(fruits) to be more clear, but giving a negative index in python works by starting from the back of the array and counting backwards. So in effect, you'd be just starting somewhere randomly in the array - set by randomOffset, and then takign al lthe subsequent items.
A deque is built for this operation: collections.deque
Instead of using fruits[index:], you could create a deque and rotate it:
from collections import deque
fruit_deque = deque(fruits)
fruit_deque.rotate(-index)
for fruit in fruit_deque:
print fruit
Another option is cycle and islice:
from itertools import cycle, islice
fruit_cycle = cycle(fruits)
fruit_slice = islice(fruit_cycle, index, index + len(fruits))
for fruit in fruit_slice:
print fruit
You could wrap around more than once with this method, by replacing len(fruits) with any number (or use islice(fruit_cycle, index, None) to cycle indefinitely).
It looks like you're just trying to visit the list in random order (since your two sample outputs aren't both rotations of the original list).
In that case, may I suggest random.shuffle?
import random
randlist = fruits[:]
random.shuffle(randlist)
for i in randlist:
print i
This prints the list in a random order.
You could avoid a for loop and splice up to the index then reverse the elements greater than the index
>>> fruits = ['banana', 'apple', 'mango']
>>> index = 0
>>> fruits[index:] + fruits[:index][::-1]
['banana', 'apple', 'mango']
>>> index = 1
>>> fruits[index:] + fruits[:index][::-1]
['apple', 'mango', 'banana']
>>> index = 2
>>> fruits[index:] + fruits[:index][::-1]
['mango', 'apple', 'banana']
index, which is going to screw you up. Second, you should be able to use the%modulus operator to get that working, I would think.