Moving Zeros To The End: Why does my Python Code fail the test in CodeWars?

Question

Problem

Link to the problem: https://www.codewars.com/kata/52597aa56021e91c93000cb0/train/python

Write an algorithm that takes an array and moves all of the zeros to the end, preserving the order of the other elements.

move_zeros([false,1,0,1,2,0,1,3,"a"]) # returns[false,1,1,2,1,3,"a",0,0]

My code:

def move_zeros(array):
    zero_count = array.count(0)
    array1 = list(filter(lambda a: a != 0, array)) + [0 for i in range(zero_count)]
    return array1

Sample Tests:

Test.describe("Basic tests")
Test.assert_equals(move_zeros([1,2,0,1,0,1,0,3,0,1]),[ 1, 2, 1, 1, 3, 1, 0, 0, 0, 0 ])
Test.assert_equals(move_zeros([9,0.0,0,9,1,2,0,1,0,1,0.0,3,0,1,9,0,0,0,0,9]),[9,9,1,2,1,1,3,1,9,9,0,0,0,0,0,0,0,0,0,0])
Test.assert_equals(move_zeros(["a",0,0,"b","c","d",0,1,0,1,0,3,0,1,9,0,0,0,0,9]),["a","b","c","d",1,1,3,1,9,9,0,0,0,0,0,0,0,0,0,0])
Test.assert_equals(move_zeros(["a",0,0,"b",None,"c","d",0,1,False,0,1,0,3,[],0,1,9,0,0,{},0,0,9]),["a","b",None,"c","d",1,False,1,3,[],1,9,{},9,0,0,0,0,0,0,0,0,0,0])
Test.assert_equals(move_zeros([0,1,None,2,False,1,0]),[1,None,2,False,1,0,0])
Test.assert_equals(move_zeros(["a","b"]),["a","b"])
Test.assert_equals(move_zeros(["a"]),["a"])
Test.assert_equals(move_zeros([0,0]),[0,0])
Test.assert_equals(move_zeros([0]),[0])
Test.assert_equals(move_zeros([False]),[False])
Test.assert_equals(move_zeros([]),[])

My Output after running:

Test Passed
Test Passed
Test Passed
['a', 'b', None, 'c', 'd', 1, 1, 3, [], 1, 9, {}, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] should equal ['a', 'b', None, 'c', 'd', 1, False, 1, 3, [], 1, 9, {}, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
[1, None, 2, 1, 0, 0, 0] should equal [1, None, 2, False, 1, 0, 0]
Test Passed
Test Passed
Test Passed
Test Passed
Test Passed
Test Passed

My Question:

Why does my answer fail the 2 tests?

Just swap in a loop, and keep track the last non-zero position. — Eric, Apr 30 '20 at 12:24
@EricWang Thank you very much for the idea :) Please provide a solution with code. — NewbieProgrammer, May 01 '20 at 08:09
Does this answer your question? [Moving Zeros To The End: Failing the test in CodeWars?](https://stackoverflow.com/questions/61661462/moving-zeros-to-the-end-failing-the-test-in-codewars) — anatolyg, May 07 '20 at 16:55

Psytho · Answer 1 · 2020-04-30T10:53:43.633

0

Because you just drop out all Falses in a != 0. False is 0 and 0 is False.

Further details: Is False == 0 and True == 1 an implementation detail or is it guaranteed by the language?

edited Apr 30 '20 at 10:53

answered Apr 30 '20 at 10:52

Psytho

3,313
2
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Lev Izraelit · Accepted Answer · 2020-05-01T08:12:37.407

0

In python, the values True and False behave as equivalent to 1 and 0 when compared to integers. See the section under numbers.Integral in the The standard type hierarchy. This means that when counting the zeroes, False will be counted as well, and in the lambda:

lambda a: a != 0

The comparison of a != 0 will filter out both 0 and False. One way to correct this is to modify the count to also be a filter, and to check in both lambdas that a is not a boolean:

def move_zeros(array):
    zero_list = list(filter(lambda a: a == 0 and not isinstance(a, bool), array))
    array1 = list(filter(lambda a: a != 0 or isinstance(a, bool), array)) + zero_list
    return array1

edited May 01 '20 at 08:12

answered Apr 30 '20 at 11:00

Lev Izraelit

512
4
14

Could you please update my code? It would be helpful :) – NewbieProgrammer Apr 30 '20 at 11:25
Updated the code and explanation to also include the count, since `count(0)` would count both zeroes and `False` values. – Lev Izraelit May 01 '20 at 08:13

score 0 · Answer 3 · answered May 01 '20 at 05:26

0

change all values a string and then perform the function

answered May 01 '20 at 05:26

user13445889

1

1

Nice idea. But still I would prefer a solution with code – NewbieProgrammer May 01 '20 at 05:30

score 0 · Answer 4 · answered May 01 '20 at 07:03

0

You need

def move_zeros(array):
    zero_count = array.count(0)
    array1 = list(filter(lambda a: a != 0 or isinstance(a, bool), array)) + [0 for i in range(zero_count)]
    return array1

answered May 01 '20 at 07:03

Bhaskar

1,838
1
16
29

That didn't work. Please add the code after testing – NewbieProgrammer May 01 '20 at 08:06
['a', 'b', None, 'c', 'd', 1, False, 1, 3, [], 1, 9, {}, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] should equal ['a', 'b', None, 'c', 'd', 1, False, 1, 3, [], 1, 9, {}, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0] – NewbieProgrammer May 01 '20 at 08:06
[1, None, 2, False, 1, 0, 0, 0] should equal [1, None, 2, False, 1, 0, 0] – NewbieProgrammer May 01 '20 at 08:06

score 0 · Answer 5 · answered Oct 26 '21 at 02:52

0

I found this answer and it works. I just don't understand how it works.

def move_zeros(a):
    a.sort(key=lambda v: v == 0)
    return a

answered Oct 26 '21 at 02:52

Bryan Hildreth

29
1
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Moving Zeros To The End: Why does my Python Code fail the test in CodeWars?

5 Answers5