Remove adjacent duplicate elements from a list [duplicate]

Answer 1

Extremely elegant solution from Google (source is here: https://developers.google.com/edu/python/exercises/basic):

def remove_adjacent(nums):
    result = []
    for num in nums:
        if len(result) == 0 or num != result[-1]:
            result.append(num)
    return result

Answer 2

def removeDupAdj2(a):
    b=[]
    for i in reversed(range(1,len(a))):
        if(a[i-1] == a[i]):
            del(a[i])
            #print(a)
    return a

a = [int(i) for i in '1 2 3 3 4 4 3 5 4 4 6 6 6 7 8 8 8 9 1 1 0 0'.split(' ')]
a

res = removeDupAdj2(a)
res

Answer 3

@katrielalex's solution is more pythonic, but if you did need to modify the list in-place without making a copy, you could use a while loop and break when you catch an IndexError. e.g.

nums = [1,1,1,2,2,3,3,3,5,5,1,1,1]
def remove_adjacent(nums):
    """Removes adjacent items by modifying "nums" in-place. Returns None!"""
    i = 0
    while True:
        try:
            if nums[i] == nums[i+1]:
                # Letting you figure this part out, 
                # as it's a homework question
        except IndexError:
            break
print nums
remove_adjacent(nums)
print nums

Edit: pastebin of one way to do it here, in case you get stuck and want to know..

Answer 4

Try this:

def remove_adjacent(nums):
  result = []
  if len(nums) > 0:
    result = [nums[0]]
    for i in range(len(nums)-1):
        if nums[i] != nums[i+1]:
            result.append(nums[i+1])

  return result

Answer 5

You can modify a list you're iterating over if you use indices explicitly:

def remove_adjacent(l):
  if len(l)<2:
    return l
  prev,i = l[0],1
  while i < len(l):
    if l[i] == prev:
      del l[i]
    else:
      prev = l[i]
      i += 1

It doesn't work with iterators because iterators don't "know" how to modify the index when you remove arbitrary elements, so it's easier to just forbid it. Some languages have iterators with functions to remove the "current item".

Answer 6

Well, katrielalex is right about itertools, but the OP seems to be rather more interested (or should be!) in learning to manipulate the basics of the built-in data structures. As for manipulating a list in place, it does need thought, but my recommendation would be to read through this section of the documentation and try a few list methods (hint: list.pop(), list.remove(), and learn everything about slices.)

The posted code could be simplified, by the way (you should however add handling of error conditions):

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