Let's say I have a list:
n1 = [20, 21, 22, 23, 24]
and I want to iterate through the list and print the first three elements, then the next three elements of the sequence, up to the end. That is, I want this to be output:
20, 21, 22
21, 22, 23
22, 23, 24
How can I do this efficiently in Python?
You can try this:
n1 = [20, 21, 22, 23, 24]
listing = [', '.join(map(str, n1[i:i+3])) for i in range(len(n1)-2)]
for l in listing:
print(l)
Output:
20, 21, 22
21, 22, 23
22, 23, 24
One way is to chunk your list and print. A generator function helps make this efficient, explicit and adaptable. Courtesy of @Ned Batchelder (upvote there).
def chunks(l, n):
"""Yield successive n-sized chunks from l."""
for i in range(0, len(l) - (n-1)):
yield l[i:i + n]
n1 = [20, 21, 22, 23, 24, 25]
for lst in chunks(n1, 3):
print(' '.join(map(str, lst)))
# 20 21 22
# 21 22 23
# 22 23 24
# 23 24 25
If you only want to print out chunks of length 3, you can use zip() here:
n1 = [20, 21, 22, 23, 24]
for x, y, z in zip(n1, n1[1:], n1[2:]):
print(x, y, z)
Which Outputs:
20 21 22
21 22 23
22 23 24
If you want to print out any sized chunks, you can use collections.deque:
from collections import deque
from itertools import islice
def chunks(lst, n):
queue = deque(lst)
while len(queue) >= n:
yield list(islice(queue, 0, n))
queue.popleft()
n1 = [20, 21, 22, 23, 24]
for x in chunks(n1, 3):
print(*x)
# 20 21 22
# 21 22 23
# 22 23 24
