Add additional str accessor methods for DataArray (#4622)

* add type hints for the str accessor class

* allow str accessors to use regular expression objects for regular expressions

* implement casefold and normalize str accessor functions

* implement one-to-many str accessor functions

* implement cat, join, format, +, *, and %

* support elementwise operations in many str accessor functions

* update whats-new.rst, api.rst, and api-hidden.rst

* test fixes

* implement requested fixes

* more fixes

* typing fixes

* fix docstring

* fix more docstring

* remove encoding header

Co-authored-by: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>

doc/api-hidden.rst

@@ -324,14 +324,21 @@
    core.accessor_dt.TimedeltaAccessor.seconds
 
    core.accessor_str.StringAccessor.capitalize
+   core.accessor_str.StringAccessor.casefold
+   core.accessor_str.StringAccessor.cat
    core.accessor_str.StringAccessor.center
    core.accessor_str.StringAccessor.contains
    core.accessor_str.StringAccessor.count
    core.accessor_str.StringAccessor.decode
    core.accessor_str.StringAccessor.encode
    core.accessor_str.StringAccessor.endswith
+   core.accessor_str.StringAccessor.extract
+   core.accessor_str.StringAccessor.extractall
    core.accessor_str.StringAccessor.find
+   core.accessor_str.StringAccessor.findall
+   core.accessor_str.StringAccessor.format
    core.accessor_str.StringAccessor.get
+   core.accessor_str.StringAccessor.get_dummies
    core.accessor_str.StringAccessor.index
    core.accessor_str.StringAccessor.isalnum
    core.accessor_str.StringAccessor.isalpha
@@ -342,20 +349,26 @@
    core.accessor_str.StringAccessor.isspace
    core.accessor_str.StringAccessor.istitle
    core.accessor_str.StringAccessor.isupper
+   core.accessor_str.StringAccessor.join
    core.accessor_str.StringAccessor.len
    core.accessor_str.StringAccessor.ljust
    core.accessor_str.StringAccessor.lower
    core.accessor_str.StringAccessor.lstrip
    core.accessor_str.StringAccessor.match
+   core.accessor_str.StringAccessor.normalize
    core.accessor_str.StringAccessor.pad
+   core.accessor_str.StringAccessor.partition
    core.accessor_str.StringAccessor.repeat
    core.accessor_str.StringAccessor.replace
    core.accessor_str.StringAccessor.rfind
    core.accessor_str.StringAccessor.rindex
    core.accessor_str.StringAccessor.rjust
+   core.accessor_str.StringAccessor.rpartition
+   core.accessor_str.StringAccessor.rsplit
    core.accessor_str.StringAccessor.rstrip
    core.accessor_str.StringAccessor.slice
    core.accessor_str.StringAccessor.slice_replace
+   core.accessor_str.StringAccessor.split
    core.accessor_str.StringAccessor.startswith
    core.accessor_str.StringAccessor.strip
    core.accessor_str.StringAccessor.swapcase

doc/api.rst

@@ -420,38 +420,58 @@ String manipulation
    :toctree: generated/
    :template: autosummary/accessor_method.rst
 
+   DataArray.str._apply
+   DataArray.str._padder
+   DataArray.str._partitioner
+   DataArray.str._re_compile
+   DataArray.str._splitter
+   DataArray.str._stringify
    DataArray.str.capitalize
+   DataArray.str.casefold
+   DataArray.str.cat
    DataArray.str.center
    DataArray.str.contains
    DataArray.str.count
    DataArray.str.decode
    DataArray.str.encode
    DataArray.str.endswith
+   DataArray.str.extract
+   DataArray.str.extractall
    DataArray.str.find
+   DataArray.str.findall
+   DataArray.str.format
    DataArray.str.get
+   DataArray.str.get_dummies
    DataArray.str.index
    DataArray.str.isalnum
    DataArray.str.isalpha
    DataArray.str.isdecimal
    DataArray.str.isdigit
+   DataArray.str.islower
    DataArray.str.isnumeric
    DataArray.str.isspace
    DataArray.str.istitle
    DataArray.str.isupper
+   DataArray.str.join
    DataArray.str.len
    DataArray.str.ljust
    DataArray.str.lower
    DataArray.str.lstrip
    DataArray.str.match
+   DataArray.str.normalize
    DataArray.str.pad
+   DataArray.str.partition
    DataArray.str.repeat
    DataArray.str.replace
    DataArray.str.rfind
    DataArray.str.rindex
    DataArray.str.rjust
+   DataArray.str.rpartition
+   DataArray.str.rsplit
    DataArray.str.rstrip
    DataArray.str.slice
    DataArray.str.slice_replace
+   DataArray.str.split
    DataArray.str.startswith
    DataArray.str.strip
    DataArray.str.swapcase

doc/whats-new.rst

@@ -27,6 +27,22 @@ New Features
 - Support for `dask.graph_manipulation
   <https://docs.dask.org/en/latest/graph_manipulation.html>`_ (requires dask >=2021.3)
   By `Guido Imperiale <https://github.com/crusaderky>`_
+- Many of the arguments for the :py:attr:`DataArray.str` methods now support
+  providing an array-like input. In this case, the array provided to the
+  arguments is broadcast against the original array and applied elementwise.
+- :py:attr:`DataArray.str` now supports `+`, `*`, and `%` operators. These
+  behave the same as they do for :py:class:`str`, except that they follow
+  array broadcasting rules.
+- A large number of new :py:attr:`DataArray.str` methods were implemented,
+  :py:meth:`DataArray.str.casefold`, :py:meth:`DataArray.str.cat`,
+  :py:meth:`DataArray.str.extract`, :py:meth:`DataArray.str.extractall`,
+  :py:meth:`DataArray.str.findall`, :py:meth:`DataArray.str.format`,
+  :py:meth:`DataArray.str.get_dummies`, :py:meth:`DataArray.str.islower`,
+  :py:meth:`DataArray.str.join`, :py:meth:`DataArray.str.normalize`,
+  :py:meth:`DataArray.str.partition`, :py:meth:`DataArray.str.rpartition`,
+  :py:meth:`DataArray.str.rsplit`, and  :py:meth:`DataArray.str.split`.
+  A number of these methods allow for splitting or joining the strings in an
+  array. (:issue:`4622`)
 - Thanks to the new pluggable backend infrastructure external packages may now
   use the ``xarray.backends`` entry point to register additional engines to be used in
   :py:func:`open_dataset`, see the documentation in :ref:`add_a_backend`
@@ -36,6 +52,7 @@ New Features
   developed by `B-Open <https://www.bopen.eu>`_.
   By `Aureliana Barghini <https://github.com/aurghs>`_ and `Alessandro Amici <https://github.com/alexamici>`_.
 
+
 Breaking changes
 ~~~~~~~~~~~~~~~~
 - :py:func:`open_dataset` and :py:func:`open_dataarray` now accept only the first argument