Comparing Value of List Index and Integer in Second List

Question

I'm trying to work through my first Python program (I just began taking a class for Python a month or so ago). Right now, I'm only allowed to use the standard library, but I can import the random library as well.

What I'm trying to do is compare two lists. One, is a list of random numbers (which I already have figured out) and the second one is a list of 1's and 0's. 1 meaning that the number in the first list needs to be replaced with a new random number. 0 Meaning they want to keep that number.

Could someone help me out and kind of explain their logic through it? I'm at a loss right now, and would really appreciate any help you could give me.

Here's what I have so far:

def replaceValues(distList, indexList):
    for i in range (1,len(indexList)):
         if indexList[i] = int(1):

Then I get kind of lost.

Thanks!

What have you tried so far? And, are both lists inputs, or do you have to generate them? — Joan Smith
– Joan Smith, Commented Feb 26, 2014 at 13:56
@JoanSmith Honestly, I'm kind of lost, even if just a starting point would be great. And both lists are input lists. — user3288734
– user3288734, Commented Feb 26, 2014 at 13:59

Thomas Orozco · Accepted Answer · 2014-02-26 14:04:53Z

4

Use enumerate. It lets you iterate on a list with an index:

import random

control_list = [1, 0, 1]  # Your 0's and 1's
numbers_list = [1, 2, 3]  # Your random numbers


for index, control in enumerate(control_list):
    if control == 0: 
        numbers_list[index] = random.random()

print numbers_list
# [1, 0.5932577738017294, 3]

Note that this will replace the elements in numbers_list. If that's not desirable, you can create a new list and use zip, which lets you iterate over two lists in parallel:

import random

control_list = [1, 0, 1]
numbers_list = [1, 2, 3]

new_list = []
for control, number in zip(control_list, numbers_list):
    if control == 0:
        number = random.random()
    new_list.append(number)

print new_list
# [1, 0.46963935996528683, 3]

And in a single line, using a list comprehension:

l = [n if c == 1 else random.random() for n, c in zip(numbers_list, control_list)]
print l
# [1, 0.9579195229977218, 3]

edited Feb 26, 2014 at 14:04

answered Feb 26, 2014 at 13:59

Thomas Orozco

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2 Comments

user3288734 Over a year ago

when I run the top program, I receive an error that list indices must be integers and not tuple. Can you tell me what I'm doing wrong?

Thomas Orozco Over a year ago

@user3288734 Did you forget the , control part? You probably made a mistake copying the code.

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