[C++] String title case kernel

[asfimport]

Capitalizes the first character of each word in the string, like SQL initcap or Python str.title()

Reporter: Ian Cook / @ianmcook
Assignee: Eduardo Ponce / @edponce
Watchers: Rok Mihevc / @rok

Related issues:

• [C++] String algorithm library for StringArray/BinaryArray (is a child of)
• [C++] String capitalize kernel (is related to)
• [C++] String swap case kernel (is related to)

PRs and other links:

• GitHub Pull Request #10869

_{Note: This issue was originally created as ARROW-12714. Please see the migration documentation for further details.}

[asfimport]

Joris Van den Bossche / @jorisvandenbossche:
In Python, in addition to title() there is also capitalize(), which only capitalizes the first character of the string (and not every word in the string).

[asfimport]

Ian Cook / @ianmcook:
Thanks Joris; I created ARROW-12714 for capitalize()

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 10869
#10869

[asfimport]

Eduardo Ponce / @edponce:
Adding the following notes for reference purposes.

Converting words into a title form or capitalization is not a trivial task because of the complexities of natural language (acronyms, always capitalized words, special cases, non-alpha symbols, etc.). Also, there are no standard rules across libraries and different behaviors can be observed for certain inputs. In this PR, we chose to match the rules of Python's title() for its simplicity. Nevertheless, we note that its behavior differs from that of R's stringr library (str_to_title) when a word begins with numbers. This was detected in ARROW-13853.

# R stringr
> str_to_title("1Foo1") # "1foo1"
# Python
>>> "1Foo1".title() # "1Foo1"