CODEWITHSUNDEEP
pythonpython-2.6
joel
joel

Reputation: 1

linking two lists together with an iterator function in python

i have two lists, both with 128 items:

a= [0, 1, 2, 3, ...] b= [6.4, 53.8, -5.2, 7.1, ...]

i have to run list b through two checks:

  1. is b[n]>50.0
  2. is b[n]<0

if check1 is true, than b[n]=b[n]-50, AND a[n]=a[n]+1 if check2 is true, than b[n]=b[n]+100, AND a[n]=a[n]-1

i can't figure out how to tie the two items in each list together so that a change in list b[n] triggers a change also in list a[n]

using this example, after running these lists through the 2 checks:

a= [0, 2, 1, 3, ...] b= [6.4, 3.8, 94.8, 7.1, ...]

i'm only weeks into programming with python and i have absolutely no previous experience with coding. i've been reading about iterators, maps, for loops, etc but i can't seem to get the language right for this sequence.

it seems easy but i'm stuck!

thanks,

joel.

Upvotes: 0

Views: 1183

Answers (2)

Hugh Bothwell
Hugh Bothwell

Reputation: 56674

Is there anything wrong with just

for i in range(len(a)):
    if b[i] > 50.0:
        b[i] -= 50.0
        a[i] += 1
    elif b[i] < 0.0:
        b[i] += 100.0
        a[i] -= 1

Upvotes: 3

Karl Knechtel
Karl Knechtel

Reputation: 61617

Produce pairs of corresponding items from the two lists with zip and process each pair. You can use a generator comprehension to get all the processed pairs, and zip again to get lists back.

def process(a, b):
    if b > 50:
        a += 1
        b -= 50
    elif b < 0:
        a -= 1
        b += 100
    return (a, b)

def process_all(as, bs):
    # Notice the '*' here. 'zip' takes multiple arguments;
    # the '*' forces evaluation of the generator, and expands the resulting
    # sequence into several arguments.
    return zip(*(process(a, b) for (a, b) in zip(as, bs)))

Upvotes: 4

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