.. code:: ipython3

    from functools import partial
    from rpy2.ipython import html
    html.html_rdataframe=partial(html.html_rdataframe, table_class="docutils")

``R`` and ``pandas`` data frames
================================

R ``data.frame`` and :class:``pandas.DataFrame`` objects share a lot of
conceptual similarities, and :mod:``pandas`` chose to use the class name
``DataFrame`` after R objects.

In a nutshell, both are sequences of vectors (or arrays) of consistent
length or size for the first dimension (the “number of rows”). if coming
from the database world, an other way to look at them is column-oriented
data tables, or data table API.

rpy2 is providing an interface between Python and R, and a convenience
conversion layer between :class:``rpy2.robjects.vectors.DataFrame`` and
:class:``pandas.DataFrame`` objects, implemented in
:mod:``rpy2.robjects.pandas2ri``.

.. code:: ipython3

    import pandas as pd
    import rpy2.robjects as ro
    from rpy2.robjects.packages import importr 
    from rpy2.robjects import pandas2ri

From ``pandas`` to ``R``
------------------------

Pandas data frame:

.. code:: ipython3

    pd_df = pd.DataFrame({'int_values': [1,2,3],
                          'str_values': ['abc', 'def', 'ghi']})
    
    pd_df




.. raw:: html

    <div>
    <style scoped>
        .dataframe tbody tr th:only-of-type {
            vertical-align: middle;
        }
    
        .dataframe tbody tr th {
            vertical-align: top;
        }
    
        .dataframe thead th {
            text-align: right;
        }
    </style>
    <table border="1" class="dataframe">
      <thead>
        <tr style="text-align: right;">
          <th></th>
          <th>int_values</th>
          <th>str_values</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <th>0</th>
          <td>1</td>
          <td>abc</td>
        </tr>
        <tr>
          <th>1</th>
          <td>2</td>
          <td>def</td>
        </tr>
        <tr>
          <th>2</th>
          <td>3</td>
          <td>ghi</td>
        </tr>
      </tbody>
    </table>
    </div>



R data frame converted from a ``pandas`` data frame:

.. code:: ipython3

    with (ro.default_converter + pandas2ri.converter).context():
      r_from_pd_df = ro.conversion.get_conversion().py2rpy(pd_df)
    
    r_from_pd_df




.. raw:: html

    
    <span>R/rpy2 DataFrame (3 x 2)</span>
    <table>
      <thead>
        <tr>
    
          <th>int_values</th>
    
          <th>str_values</th>
    
        </tr>
      </thead>
      <tbody>
    
      <tr>
    
        <td>
          ...
        </td>
    
        <td>
          ...
        </td>
    
      </tr>
    
      </tbody>
    </table>




The conversion is automatically happening when calling R functions. For
example, when calling the R function ``base::summary``:

.. code:: ipython3

    base = importr('base')
    
    with (ro.default_converter + pandas2ri.converter).context():
      df_summary = base.summary(pd_df)
    print(df_summary)


.. parsed-literal::

       int_values   str_values       
     Min.   :1.0   Length:3          
     1st Qu.:1.5   Class :character  
     Median :2.0   Mode  :character  
     Mean   :2.0                     
     3rd Qu.:2.5                     
     Max.   :3.0                     
    


Note that a ``ContextManager`` is used to limit the scope of the
conversion. Without it, rpy2 will not know how to convert a pandas data
frame:

.. code:: ipython3

    try:
      df_summary = base.summary(pd_df)
    except NotImplementedError as nie:
      print('NotImplementedError:')
      print(nie)


.. parsed-literal::

    NotImplementedError:
    Conversion 'py2rpy' not defined for objects of type '<class 'pandas.core.frame.DataFrame'>'


From ``R`` to ``pandas``
------------------------

Starting from an R data frame this time:

.. code:: ipython3

    r_df = ro.DataFrame({'int_values': ro.IntVector([1,2,3]),
                         'str_values': ro.StrVector(['abc', 'def', 'ghi'])})
    
    r_df




.. raw:: html

    
    <span>R/rpy2 DataFrame (3 x 2)</span>
    <table>
      <thead>
        <tr>
    
          <th>int_values</th>
    
          <th>str_values</th>
    
        </tr>
      </thead>
      <tbody>
    
      <tr>
    
        <td>
          ...
        </td>
    
        <td>
          ...
        </td>
    
      </tr>
    
      </tbody>
    </table>




It can be converted to a pandas data frame using the same converter:

.. code:: ipython3

    with (ro.default_converter + pandas2ri.converter).context():
      pd_from_r_df = ro.conversion.get_conversion().rpy2py(r_df)
    
    pd_from_r_df




.. raw:: html

    <div>
    <style scoped>
        .dataframe tbody tr th:only-of-type {
            vertical-align: middle;
        }
    
        .dataframe tbody tr th {
            vertical-align: top;
        }
    
        .dataframe thead th {
            text-align: right;
        }
    </style>
    <table border="1" class="dataframe">
      <thead>
        <tr style="text-align: right;">
          <th></th>
          <th>int_values</th>
          <th>str_values</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <th>1</th>
          <td>1</td>
          <td>abc</td>
        </tr>
        <tr>
          <th>2</th>
          <td>2</td>
          <td>def</td>
        </tr>
        <tr>
          <th>3</th>
          <td>3</td>
          <td>ghi</td>
        </tr>
      </tbody>
    </table>
    </div>



Date and time objects
---------------------

.. code:: ipython3

    pd_df = pd.DataFrame({
        'Timestamp': pd.date_range('2017-01-01 00:00:00', periods=10, freq='s')
        })
        
    pd_df




.. raw:: html

    <div>
    <style scoped>
        .dataframe tbody tr th:only-of-type {
            vertical-align: middle;
        }
    
        .dataframe tbody tr th {
            vertical-align: top;
        }
    
        .dataframe thead th {
            text-align: right;
        }
    </style>
    <table border="1" class="dataframe">
      <thead>
        <tr style="text-align: right;">
          <th></th>
          <th>Timestamp</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <th>0</th>
          <td>2017-01-01 00:00:00</td>
        </tr>
        <tr>
          <th>1</th>
          <td>2017-01-01 00:00:01</td>
        </tr>
        <tr>
          <th>2</th>
          <td>2017-01-01 00:00:02</td>
        </tr>
        <tr>
          <th>3</th>
          <td>2017-01-01 00:00:03</td>
        </tr>
        <tr>
          <th>4</th>
          <td>2017-01-01 00:00:04</td>
        </tr>
        <tr>
          <th>5</th>
          <td>2017-01-01 00:00:05</td>
        </tr>
        <tr>
          <th>6</th>
          <td>2017-01-01 00:00:06</td>
        </tr>
        <tr>
          <th>7</th>
          <td>2017-01-01 00:00:07</td>
        </tr>
        <tr>
          <th>8</th>
          <td>2017-01-01 00:00:08</td>
        </tr>
        <tr>
          <th>9</th>
          <td>2017-01-01 00:00:09</td>
        </tr>
      </tbody>
    </table>
    </div>



.. code:: ipython3

    with (ro.default_converter + pandas2ri.converter).context():
      r_from_pd_df = ro.conversion.py2rpy(pd_df)
    
    r_from_pd_df




.. raw:: html

    
    <span>R/rpy2 DataFrame (10 x 1)</span>
    <table>
      <thead>
        <tr>
    
          <th>Timestamp</th>
    
        </tr>
      </thead>
      <tbody>
    
      <tr>
    
        <td>
          ...
        </td>
    
      </tr>
    
      </tbody>
    </table>




The timezone used for conversion is the system’s default timezone unless
``rpy2.robjects.vectors.default_timezone`` is specified… or unless the
time zone is specified in the original time object:

.. code:: ipython3

    pd_tz_df = pd.DataFrame({
        'Timestamp': pd.date_range('2017-01-01 00:00:00', periods=10, freq='s',
                                   tz='UTC')
        })
        
    with (ro.default_converter + pandas2ri.converter).context():
      r_from_pd_tz_df = ro.conversion.py2rpy(pd_tz_df)
    
    r_from_pd_tz_df




.. raw:: html

    
    <span>R/rpy2 DataFrame (10 x 1)</span>
    <table>
      <thead>
        <tr>
    
          <th>Timestamp</th>
    
        </tr>
      </thead>
      <tbody>
    
      <tr>
    
        <td>
          ...
        </td>
    
      </tr>
    
      </tbody>
    </table>