If I have a list of lists and just want to manipulate an individual item in that list, how would I go about doing that?
For example:
List1 = [[10,13,17],[3,5,1],[13,11,12]]
What if I want to take a value (say 50) and look just at the first sublist in List1, and subtract 10 (the first value), then add 13, then subtract 17?
You can access the elements in a list-of-lists by first specifying which list you're interested in and then specifying which element of that list you want. For example, 17 is element 2 in list 0, which is list1[0][2]:
>>> list1 = [[10,13,17],[3,5,1],[13,11,12]]
>>> list1[0][2]
17
So, your example would be
50 - list1[0][0] + list1[0][1] - list1[0][2]
You can use itertools.cycle:
>>> from itertools import cycle
>>> lis = [[10,13,17],[3,5,1],[13,11,12]]
>>> cyc = cycle((-1, 1))
>>> 50 + sum(x*next(cyc) for x in lis[0]) # lis[0] is [10,13,17]
36
Here the generator expression inside sum would return something like this:
>>> cyc = cycle((-1, 1))
>>> [x*next(cyc) for x in lis[0]]
[-10, 13, -17]
You can also use zip here:
>>> cyc = cycle((-1, 1))
>>> [x*y for x, y in zip(lis[0], cyc)]
[-10, 13, -17]
This code will print each individual number:
for myList in [[10,13,17],[3,5,1],[13,11,12]]:
for item in myList:
print(item)
Or for your specific use case:
((50 - List1[0][0]) + List1[0][1]) - List1[0][2]
List1 = [[10,-13,17],[3,5,1],[13,11,12]]
num = 50
for i in List1[0]:num -= i
print num
50 - List1[0][0] + List[0][1] - List[0][2]
List[0] gives you the first list in the list (try out print List[0]). Then, you index into it again to get the items of that list. Think of it this way: (List1[0])[0].
for l in list1:
val = 50 - l[0] + l[1] - l[2]
print "val:", val
Loop through list and do operation on the sublist as you wanted.
new_list = list(zip(*old_list)))
*old_list unpacks old_list into multiple lists and zip picks corresponding nth element from each list and list packs them back.
