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Python | Sort tuple based on occurrence of first element
• Last Updated : 08 Apr, 2019

Given a list of tuples, write a Python program to sort the list based on the occurrence of first element of tuples.

Examples:

```Input : [(1, 'Jake'), (2, 'Bob'), (1, 'Cara')]
Output : [(1, 'Jake', 'Cara', 2), (2, 'Bob', 1)]

Input : [('b', 'ball'), ('a', 'arm'), ('b', 'b'), ('a', 'ant')]
Output : [('a', 'arm', 'ant', 2), ('b', 'ball', 'b', 2)]
```

Approach #1 : using `dict.fromkeys`

The `fromkeys()` method returns a new dictionary with the given sequence of elements as the keys of the dictionary. Now once we store the new dictionary in ‘dct’ we can easily iterate over ‘dct’ elements and output the desired elements.

 `# Python3 program to Sort tuple based ``# on occurrence of first element``def` `sortOnOccurence(lst):``    ``dct ``=` `{}``    ``for` `i, j ``in` `lst:``        ``dct.setdefault(i, []).append(j)``    ``return``([(i, ``*``dict``.fromkeys(j), ``len``(j))``                 ``for` `i, j ``in` `dct.items()])`` ` `# Driver code``lst ``=` `[(``1``, ``'Jake'``), (``2``, ``'Bob'``), (``1``, ``'Cara'``)]``print``(sortOnOccurence(lst))`
Output:

```[(1, 'Cara', 'Jake', 2), (2, 'Bob', 1)]
```

Approach #2 : `OrderedDict` from collections module

This method is an alternative to the above-mentioned approach. We follow similar approach but with a slight change, concatenate the tuples while iterating through ‘dct’ using OrderedDict.

 `# Python3 program to Sort tuple based ``# on occurrence of first element``from` `collections ``import` `OrderedDict`` ` `def` `sortOnOccurence(lst):``    ``dct ``=` `{}``    ``for` `i, j ``in` `lst:``        ``dct.setdefault(i, []).append(j)``    ``return``([(k, ) ``+` `tuple``(OrderedDict.fromkeys(v)) ``+` `(``len``(v), )``    ``for` `k, v ``in` `dct.items()])`` ` `# Driver code``lst ``=` `[(``1``, ``'Jake'``), (``2``, ``'Bob'``), (``1``, ``'Cara'``)]``print``(sortOnOccurence(lst))`
Output:
```[(1, 'Jake', 'Cara', 2), (2, 'Bob', 1)]
```

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