Nested FOR loops - coding challenge

Question

I am learning python using STEPIK and I am facing this:

I want on every iteration of the inside for loop sum the values of predicted_growth list with the value of cases list, save it in some temporary variable and print it. Click on the link for the full challenge.

This is my code so far:

def predict_cases(cases, predicted_growth):
    print()
    result = []
    for i in range(len(cases)):
        for j in range(len(predicted_growth)):
            result = cases[i] + predicted_growth[j]
            print(result, end = " ")
        print()


cases = [12508, 9969, 310595, 57409]
predicted_growth = [100, 200, 300]

predict_cases(cases, predicted_growth)

This is the output of the function I should be getting:

[12608, 10069, 310695, 57509]
[12808, 10269, 310895, 57709]
[13108, 10569, 311195, 58009]

Instead I am getting this:

12608 12708 12808 
10069 10169 10269 
310695 310795 310895 
57509 57609 57709

python_user · Accepted Answer · 2021-04-16 13:35:53Z

1

You can use a loop with an inner list comprehension.

def predict_cases(cases, predicted_growth):
    res = [] # this will hold the results

    for growth_rate in predicted_growth: # outer loop to iterate the growth rate
        prev = res[-1] if res else cases # get the previously computed result, if there is no such result get initial cases (`cases`) as previously computed result
        res.append([growth_rate + i for i in prev]) # list comprehension to add the current growth rate(`growth_rate`) to the previous cases

    for result in res: # iterate through `res` list
        print(result) # print the result

cases = [12508, 9969, 310595, 57409]
predicted_growths = [100, 200, 300]
predict_cases(cases, predicted_growths)

Output

[12608, 10069, 310695, 57509]
[12808, 10269, 310895, 57709]
[13108, 10569, 311195, 58009]

edited Apr 16, 2021 at 13:35

answered Apr 16, 2021 at 13:20

python_user

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2 Comments

Boris AllAboutAnyth Over a year ago

That's perfect, but to be honest I don't understand most of the lines. I will have to dive into list comprehension. Thank you

python_user Over a year ago

I will add in a comment

quamrana · Accepted Answer · 2021-04-16 13:21:04Z

0

You just have your for loops inside out:

def predict_cases(cases, predicted_growth):
    print()
    growth = 0
    for j in predicted_growth:
        growth += j;
        result = []
        for i in cases:
            result.append(growth + i)
        print(result)


cases = [12508, 9969, 310595, 57409]
predicted_growth = [100, 200, 300]

predict_cases(cases, predicted_growth)

Output:

[12608, 10069, 310695, 57509]
[12808, 10269, 310895, 57709]
[13108, 10569, 311195, 58009]

edited Apr 16, 2021 at 13:21

answered Apr 16, 2021 at 13:16

quamrana

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Comments

MorganTimney · Accepted Answer · 2021-04-16 13:36:27Z

0

Lists are inherently iterable, thus for i in myList: makes it easier. List also have the .append() method, which builds your list easily. Then the aforementioned loop swap to get things in your desired order.

def predict_cases(cases, predicted_growth):

    for j in predicted_growth:
        result = []
        for i in cases:
            result.append(i + j)
        print(result)

cases = [12508, 9969, 310595, 57409]
predicted_growth = [100, 200, 300]
predict_cases(cases, predicted_growth)

answered Apr 16, 2021 at 13:36

MorganTimney

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Comments

Atalajaka · Accepted Answer · 2021-04-16 15:16:29Z

0

First, the order of the nested loops should be reversed in my opinion,as you want to print three lists, corresponding to len(predicted_growth) and not four lists, which would correspond to len(cases).

Also, you are creating the variable result as a list but then you are overwriting it with a number, which is cases[i] + predicted_growth[j], so it will always print the numbers and never the list containing them.

I got the desired output with the following function:

def test(c, p):
    print()
    growth_factor = 0
    result = []
    for i in p:
        growth_factor += i
        for j in c:
            result.append(i + growth_factor)
        print(result)
        result = []

Note that you can iterate in a list as it is shown in the for loops, without the need of specifying list[iterator], which in this example can be more comfortable in my opinion.

edited Apr 16, 2021 at 15:16

answered Apr 16, 2021 at 13:30

Atalajaka

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2 Comments

Boris AllAboutAnyth Over a year ago

Thank you, now it outputs lists, awesome! but the operation isn't simply addition its increment of a predicted_growth list member and cases. Therefore the step is not always 100 but 100, 200, 300 from the previous sum -- > [12608, 10069, 310695, 57509] [12808, 10269, 310895, 57709] [13108, 10569, 311195, 58009]

Atalajaka Over a year ago

You are right, my mistake, I read through my output too quickly. I have updated my code with the missing operations in order to get the expected output. You do need a variable which determines the current growth factor in order to properly update the resulting list.

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