CODEWITHSUNDEEP
python
He4xi
He4xi

Reputation: 47

How to loop through a list multiple times?

Can you loop through list (using range that has a step in it) over and over again until all the elements in the list are accessed by the loop?

I have the following lists:

result = []
list = ['ba', 'cb', 'dc', 'ed', 'gf', 'jh']

i want the outcome (result) to be:

result = ['dc', 'cb', 'ba', 'jh', 'gf', 'ed']

How do i make it loop through the first list, and appending each element to result list, starting from the third element and using 5 as a step, until all the elements are in the results list?

Upvotes: 1

Views: 2967

Answers (3)

nCCNcXpS35gfBn39zRzJ
nCCNcXpS35gfBn39zRzJ

Reputation: 99

A very simple solution was posted earlier, not sure why it was removed:

>>> a = ['ba', 'cb', 'dc', 'ed', 'gf', 'jh']
>>> result = [a[n] for n in range(2, -4, -1)]
>>> result
['dc', 'cb', 'ba', 'jh', 'gf', 'ed']

Upvotes: -1

Kasravnd
Kasravnd

Reputation: 107287

There is no need to loop through a list multiple times.As a more pythonic way You can use itertools.cycle and islice :

>>> from itertools import cycle,islice
>>> li= ['ba', 'cb', 'dc', 'ed', 'gf', 'jh']
>>> sl=islice(cycle(li),2,None,4)
>>> [next(sl) for _ in range(len(li))]
['dc', 'ba', 'gf', 'dc', 'ba', 'gf']

Note that in your expected output the step is 5 not 4.So if you use 5 as slice step you'll get your expected output :

>>> sl=islice(cycle(li),2,None,5)
>>> [next(sl) for _ in range(len(li))]
['dc', 'cb', 'ba', 'jh', 'gf', 'ed']

Upvotes: 7

Kevin
Kevin

Reputation: 76194

Assuming the step and the length of the list are coprime, you can do:

result = []
list = ['ba', 'cb', 'dc', 'ed', 'gf', 'jh']
start = 2
step = 5
end = start + step*len(list)
for i in range(start, end, step):
    result.append(list[i%len(list)])
print result

Result:

['dc', 'cb', 'ba', 'jh', 'gf', 'ed']

Upvotes: 4

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