I have a list of numbers go in one row like this:
0
1
0
2
0
4
and it has about thousands of rows
I want to add them up every 3 rows so the results will be like this:
1
6
I have already made the list into individual integer with this line:
k = map(lambda s: s.strip(), k)
integer = map(int, k)
How would I able to do the adding up?
Use a grouper, like from Alternative way to split a list into groups of n:
import itertools
def grouper(n, iterable, fillvalue=None):
"grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx"
args = [iter(iterable)] * n
return itertools.izip_longest(*args, fillvalue=fillvalue)
map(sum, grouper(3, interger, 0))
Note that the above code assumes python 2.x; for 3.x you'll need to use itertools.zip_longest instead.
Demo:
>>> example = [0, 1, 0, 2, 0, 4]
>>> map(sum, grouper(3, example, 0))
[1, 6]
Since you say you already have a list of numbers, then
result = [sum(data[i:i+3])for i in range(0, len(data),3)]
e.g.,
data = range(1, 16) # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16]
yields
[6, 15, 24, 33, 42]
This is probably the most pythonic:
>>> my_list = iter(my_list)
>>> map(sum, zip(my_list, my_list, my_list))
[1, 6]
Using itertools grouper recipe
>>> from itertools import izip_longest
>>> def grouper(n, iterable, fillvalue=None):
"Collect data into fixed-length chunks or blocks"
# grouper(3, 'ABCDEFG', 'x') --> ABC DEF Gxx
args = [iter(iterable)] * n
return izip_longest(fillvalue=fillvalue, *args)
>>> with open('data.txt') as fin:
for g in grouper(3, fin):
print sum(map(int, g))
1
6
Grouper and all the fancy stuff will work ... but simple list comprehension will do in this case. And it should be nice and fast! :)
>>> q = range(9)
>>> q
[0, 1, 2, 3, 4, 5, 6, 7, 8]
>>> [sum(q[3*n:3*n+3]) for n in range(len(q)/3)]
[3, 12, 21]
This will skip the remaining numbers that can't fit into a group of three:
>>> def sum_three(iterable_):
... iterable_ = iter(iterable_)
... while True:
... yield next(iterable_) + next(iterable_) + next(iterable_)
...
>>> my_list = [0, 1, 0, 2, 0, 4, 99, 1]
>>> list(sum_three(my_list))
>>> [1, 6]
sumplus Alternative way to split a list into groups of n