DataFrameGroupByColumn
======================

.. cpp:class:: pandas::DataFrameGroupByColumn

   pandas C++ class.

Example
-------

.. code-block:: cpp

   #include <pandas/pandas.h>
   using namespace pandas;

   // Use DataFrameGroupByColumn
   DataFrameGroupByColumn obj;
   // ... operations ...

Aggregation
-----------

.. list-table::
   :widths: 40 20 15 25
   :header-rows: 1

   * - Signature
     - Return Type
     - Location
     - Example
   * - ``std::vector<T> transform(std::function<std::vector<T>(const std::vector<T>&)> fn) const``
     - std::vector<T>
     - pd_groupby.h:704
     - :ref:`View <example-dataframegroupbycolumn-transform-0>`


Code Examples
-------------

The following examples are extracted from the test suite.

.. _example-dataframegroupbycolumn-transform-0:

.. dropdown:: transform (pd_test_1_all.cpp:11071)
   :class-title: example-dropdown

   .. code-block:: cpp
      :linenos:
      :lineno-start: 11061
      :emphasize-lines: 11

      
                  std::cout << " -> tests passed" << std::endl;
              }
      
              void pd_test_func_apply_series_transform() {
                  std::cout << "========= Series transform ============================";
      
                  pandas::Series<double> s({1.0, 2.0, 3.0, 4.0}, "values");
      
                  // Transform must return same shape
                  auto result = s.transform([](double x) { return x * 2 + 1; });
      
                  bool passed = true;
                  if (result.size() != s.size()) {
                      passed = false;
                      std::cout << "  [FAIL] : in pd_test_func_apply_series_transform() : size changed" << std::endl;
                      throw std::runtime_error("pd_test_func_apply_series_transform failed: size changed");
                  }
      
                  std::vector<double> expected = {3.0, 5.0, 7.0, 9.0};
                  for (size_t i = 0; i < result.size(); ++i) {