Question

Let’s say a string can be made up of the characters a, b, or c.

Is it possible through a regular expression to group the characters of a string by rules – with the most strict rules being applied first, followed by weaker rules?

For example:

• Priority rule: identify “ba” appearing together in a string.
• All remaining characters will be their own groups.

Therefore, a string such as abbadaabad would group to:

a, b, ba, d, a, a, ba, d

My thinking is that once I can set up a two-level rule set, I could create a deeper ruleset with more refined rules.

Answer 1

In an alternation rule, the first matching expression wins.

This pattern will match ba if it is found, otherwise it will match individual characters:

ba|.

Here an example usage in Python:

>>> from re import findall
>>> s = 'abbadaabad'
>>> findall(r'ba|.', s)
['a', 'b', 'ba', 'd', 'a', 'a', 'ba', 'd']