Need help on python index problems

Question

I'm trying to code a program that compares elements between two equal lengthed lists, and uses the smallest number for each element and puts it into a new list. This is my code so far:

def func_0(arr_1, arr_2) :
    arr_3 = []
    if len(arr_1) == len(arr_2) :
        for num in arr_1:
            arr_3. append (min(min(arr_1), min(arr_2) ) )
        return arr_3
    else:

        print("Try again")
print(func_0( [1, 2,3], [3, 1,5]))

I think what I need to do is add indexes for the append line, but I'm not sure how to do it. Any help will be appreciated.

Do you want to have the output you show on the image? Can you explain your objective? — bruno-uy, Jun 24 '21 at 01:50

score 2 · Answer 1 · answered Jun 24 '21 at 01:53

You should iterate both lists in parallel and compare each item individually. See this question for an explanation.

Here is a fixed version of your method:

def func_0(arr_1, arr_2) :
    arr_3 = []
    if len(arr_1) == len(arr_2) :
        for num1, num2 in zip(arr_1, arr_2):
            arr_3.append(min(num1, num2))
        return arr_3
    else:
        print("Try again")

That being said, this can be implemented in a one-liner:

def func_0(arr_1, arr_2):
    return [min(tup) for tup in zip(arr_1, arr_2)]

score 1 · Answer 2 · answered Jun 24 '21 at 01:52

You can use a list comprehension with zip.

def func_0(arr_1, arr_2) :
    if len(arr_1) == len(arr_2) :
        return [min(a,b) for a, b in zip(arr_1, arr_2)]
    else:
        print("Try again")

map could also be used.

def func_0(arr_1, arr_2) :
    if len(arr_1) == len(arr_2) :
        return list(map(min, zip(arr_1, arr_2)))
    else:
        print("Try again")

score 0 · Answer 3 · answered Jun 24 '21 at 01:52

Just compare each element:

def func_0(arr1, arr2):
    result = []
    for n1, n2 in zip(arr1, arr2):
        result.append(min([n1,n2]))
    return result

Note that zip will not break if your lists are of differing length; it will only compare over the min number of elements. This may or may not be desired behavior.

score 0 · Answer 4 · answered Jun 24 '21 at 02:30

0

If you wish to find the smallest value in each list then...


for i, num in enumerate( arr_1 ):
    if num < arr_2[ i ]:
        arr_3.append( num )
    else:
        arr_3.append( arr_2[ i ] )
print( arr_3 )

answered Jun 24 '21 at 02:30

Derek

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Need help on python index problems

4 Answers4