CODEWITHSUNDEEP
pythonlist
John
John

Reputation: 1465

Access item in a list of lists

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?

Upvotes: 67

Views: 493553

Answers (9)

Gladwin
Gladwin

Reputation: 1

list1=[[1,2,3],[4,5,6],[7,8,9]] to iterate over this list in O(n)

for ar in list1:
     i=0
     if i <len(ar)-1 :
        print(arr[i])

Upvotes: -1

S u m a n t h
S u m a n t h

Reputation: 1

to print every individual element in double list
        list1=[[1,2,3],[4,5,6],[7,8,9]]
        for i in range(len(list1)):
            for j in range(len(list1[i])):
                print(list1[i][j])

Upvotes: -1

Coddy
Coddy

Reputation: 566

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.

Upvotes: -1

Phil
Phil

Reputation: 887

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]

Upvotes: 3

Ashwini Chaudhary
Ashwini Chaudhary

Reputation: 250881

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]

Upvotes: 4

rajpy
rajpy

Reputation: 2476

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.

Upvotes: 0

Joran Beasley
Joran Beasley

Reputation: 113930

List1 = [[10,-13,17],[3,5,1],[13,11,12]]

num = 50
for i in List1[0]:num -= i
print num

Upvotes: 2

Donald Miner
Donald Miner

Reputation: 39893

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].

Upvotes: 2

arshajii
arshajii

Reputation: 129477

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]

Upvotes: 72

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