# Python groupby method to remove all consecutive duplicates

Last Updated : 28 Jul, 2022

Given a string S, remove all the consecutive duplicates. Examples:

```Input  : aaaaabbbbbb
Output : ab

Input : geeksforgeeks
Output : geksforgeks

Input : aabccba
Output : abcba```

We have existing solution for this problem please refer Remove all consecutive duplicates from the string link. We can solve this problem in python quickly using itertools.groupby() method.

### How itertools.groupby(iterable,key[optional]) works in Python?

Group by method takes two input one is iterable (list,tuple,dictionary) and second is key function which calculates keys for each element present in iterable. It returns key and iterable of grouped items. If key function not specified or is None, key defaults to an identity function and returns the element unchanged. For example,

## Python3

 `numbers ``=` `[``1``, ``1``, ``1``, ``3``, ``3``, ``2``, ``2``, ``2``, ``1``, ``1``]` `import` `itertools` `for` `(key,group) ``in` `itertools.groupby(numbers):` `    ``print` `(key,``list``(group))`

Output

```1 [1, 1, 1]
3 [3, 3]
2 [2, 2, 2]
1 [1, 1]
```

## Python3

 `# function to remove all consecutive duplicates ` `# from the string in Python `   `from` `itertools ``import` `groupby ` `def` `removeAllConsecutive(``input``): ` `    `  `    ``# group all consecutive characters based on their ` `    ``# order in string and we are only concerned ` `    ``# about first character of each consecutive substring ` `    ``# in given string, so key value will work for us ` `    ``# and we will join these keys without space to ` `    ``# generate resultant string ` `    ``result ``=` `[] ` `    ``for` `(key,group) ``in` `groupby(``input``): ` `        ``result.append(key) `   `    ``print` `(''.join(result)) ` `    `  `# Driver program ` `if` `__name__ ``=``=` `"__main__"``: ` `    ``input` `=` `'aaaaabbbbbb'` `    ``removeAllConsecutive(``input``) `

Output

```ab
```

Time complexity : O(n)
Auxiliary Space : O(n)

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