Python – Split String After K-th Occurrence of Separator

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Coding Challenge

💬 Question: Given a Python string. How to split the string after the k-th occurrence of the separator (string or character)? In other words: how to ignore the first (k-1) separator occurrences when splitting a string?

Here are three examples:

  1. 'a-b-c-d-e-f-g-h', k=2, and sep='-' should be split to ['a-b', 'c', 'd', 'e', 'f', 'g', 'h']
  2. 'helloxxxworldxxxpythonxxxisxxxgreat', k=3, and sep='xxx' should be split to ['helloxxxworldxxxpython', 'is', 'great']
  3. Border case: 'a-b', k=100, and sep='-' should be split to ['a-b']

👉 Related Tutorial: Python Split String After Second Occurrence

Solution

You can split a string after the k-th occurrence of a given character in three steps:

  1. First, split the whole string using the separator sep in s.split(sep).
  2. Second, combine the first k elements of the resulting split list using the sep.join() method call.
  3. Third, use slicing and list concatenation to create a new result list.

The following code creates a function that takes as input a string s, an integer k, and a separator string sep and splits the string at the k-th occurrence of the separator:

def my_split(s, k, sep):
    all_split = s.split(sep)
    return [sep.join(all_split[0:k])] + all_split[k:]


print(my_split('a-b-c-d-e-f-g-h', k=2, sep='-'))
# ['a-b', 'c', 'd', 'e', 'f', 'g', 'h']

print(my_split('helloxxxworldxxxpythonxxxisxxxgreat', k=3, sep='xxx'))
# ['helloxxxworldxxxpython', 'is', 'great']

print(my_split('a-b', k=100, sep='-'))
# ['a-b']

Explanations

The code does multiple things.

First, it creates a list all_split by splitting the string s using separator sep. For example, when using it on string 'a-b-c-d-e-f-g-h' and sep='-', it would return ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'].

👉 Recommended Tutorial: Python String Split

Second, it combines the first k elements using the separator string sep between them by running sep.join(all_split[0:k]).

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Third, it puts the result into a list using the square bracket notation, i.e., we get a list with one string element ['a-b'] for our example.

👉 Recommended Tutorial: How to Create a Python List?

Fourth, you concatenate this list with the remaining all_split list, ignoring the first k split results, that are already merged to ignore the first split, by using the slicing expression all_split[k:].

In our example, we get ['a-b'] and ['c', 'd', 'e', 'f', 'g', 'h'] that concatenates to ['a-b', 'c', 'd', 'e', 'f', 'g', 'h'].

👉 Recommended Tutorials: List Concatenation in Python

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