<[email protected]> wrote in message
news:[email protected]...
Hi everyone,
I seem to use this pattern alot when writing functions and I'm wondering
if there is a more efficient method. It comes up whenever I want to work
with more than one item in a list; for instance, say I want to add each
consecutive number in alist and output the new list. Ideally, I'd be able
to write:
for num in list1:
newlist.append(num+nextnum)
This doesn't work, though because there's no way to access "nextnum"
unless I implement a "count" variable like this:
count=1
for num in list1:
newlist.append(num+list1[count])
count+=1
Instead, it usually ends up easier to write:
for index in range (len(list1)-1):
newlist.append((list1[index]+list1[index+1]))
It's not a big deal to have to write the additional code, but problems
arise when I use this structure in the context of more complex functions,
when I am passing multiple lists of varying length, because it is easy to
get confused with the index numbers and I can't do anything to the last
value of the list, since I then get an "indexerror" because the function
tries to call "list[i+1]".
Is there a simpler way to do a procedure like this?
From your description, do you want:
L = [1,2,3,4,5,6] result = [3,5,6,9,11]?
I don't see anything in itertools, but this works:
def ishift(L,n):
... for i in xrange(len(L)-n+1):
... yield L[i:i+n]
...
for n in shift(L,2):
... print n
...
[1, 2]
[2, 3]
[3, 4]
[4, 5]
[5, 6]
for a,b,c in shift(L,3):
... print a,b,c
...
1 2 3
2 3 4
3 4 5
4 5 6
[sum(n) for n in ishift(L,2)]
[3, 5, 7, 9, 11]
[sum(n) for n in ishift(L,3)]
[6, 9, 12, 15]
-Mark
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