Question

Google Python Class | List Exercise –

Given a list of numbers, return a list where
all adjacent == elements have been reduced to a single element,
so [1, 2, 2, 3] returns [1, 2, 3]. You may create a new list or
modify the passed in list.

My solution using a new list is –

def remove_adjacent(nums):
  a = []
  for item in nums:
    if len(a):
      if a[-1] != item:
        a.append(item)
    else: a.append(item)        
  return a

The question even suggests that it could be done by modifying the passed in list. However, the python documentation warned against modifying elements while iterating a list using the for loop.

I am wondering what else can I try apart from iterating over the list, to get this done. I am not looking for the solution, but maybe a hint that can take me into a right direction.

UPDATE

-updated the above code with suggested improvements.

-tried the following with a while loop using suggested hints –

def remove_adjacent(nums):
  i = 1
  while i < len(nums):    
    if nums[i] == nums[i-1]:
      nums.pop(i)
      i -= 1  
    i += 1
  return nums

Answer 1

Use a generator to iterate over the elements of the list, and yield a new one only when it has changed.

itertools.groupby does exactly this.

You can modify the passed-in list if you iterate over a copy:

for elt in theList[ : ]:
    ...