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groupby()

Syntax: itertools.groupby(iterable, key_func)*

Parameters:

  • iterable: Iterable can be of any kind (list, tuple, dictionary).
  • key: A function that calculates keys for each element present in iterable.

This method calculates the keys for each element present in iterable. It returns key and iterable of grouped items.

It is still not a good description of this method, in the following example we will use a lambda function as part of the key.

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from iter import groupby

L = [("a", 1), ("a", 2), ("b", 3), ("b", 4)]

# Key function
key_func = lambda x: x[0]

for key, group in groupby(L, key_func):
    print(key + " :", list(group))

# output
#a : [('a', 1), ('a', 2)]
#b : [('b', 3), ('b', 4)]

In this case the Lambda function will extract the first element of the tuple inside the list ( the a and b ) and use them as Keys, later the same iterable will be group base on the key.