ENH: let get_dummies take a DataFrame

implement via 1d

fixup docstring, tests

add documentation

test for dicts

Author: TomAugspurger

doc/source/reshaping.rst

@@ -480,6 +480,49 @@ This function is often used along with discretization functions like ``cut``:
 
 See also :func:`Series.str.get_dummies <pandas.core.strings.StringMethods.get_dummies>`.
 
+.. versionadded:: 0.15.0
+
+:func:`get_dummies` also accepts a DataFrame. By default all categorical
+variables (categorical in the statistical sense,
+those with `object` or `categorical` dtype) are encoded as dummy variables.
+
+
+.. ipython:: python
+
+    df = pd.DataFrame({'A': ['a', 'b', 'a'], 'B': ['c', 'c', 'b'],
+                       'C': [1, 2, 3]})
+    pd.get_dummies(df)
+
+All non-object columns are included untouched in the output.
+
+You can control the columns that are encoded with the ``columns`` keyword.
+
+.. ipython:: python
+
+    pd.get_dummies(df, columns=['A'])
+
+Notice that the ``B`` column is still included in the output, it just hasn't
+been encoded. You can drop ``B`` before calling ``get_dummies`` if you don't
+want to include it in the output.
+
+As with the Series version, you can pass values for the ``prefix`` and
+``prefix_sep``. By default the column name is used as the prefix, and '_' as
+the prefix separator. You can specify ``prefix`` and ``prefix_sep`` in 3 ways
+
+- string: Use the same value for ``prefix`` or ``prefix_sep`` for each column
+  to be encoded
+- list: Must be the same length as the number of columns being encoded.
+- dict: Mapping column name to prefix
+
+.. ipython:: python
+
+    simple = pd.get_dummies(df, prefix='new_prefix')
+    simple
+    from_list = pd.get_dummies(df, prefix=['from_A', 'from_B'])
+    from_list
+    from_dict = pd.get_dummies(df, prefix={'B': 'from_B', 'A': 'from_A'})
+    from_dict
+
 Factorizing values
 ------------------
 

doc/source/v0.15.0.txt

@@ -461,7 +461,15 @@ Enhancements
 
 
 
+- The ``get_dummies`` method can now be used on DataFrames. By default only
+catagorical columns are encoded as 0's and 1's, while other columns are
+left untouched.
 
+  .. ipython:: python
+
+    df = pd.DataFrame({'A': ['a', 'b', 'a'], 'B': ['c', 'c', 'b'],
+                       'C': [1, 2, 3]})
+    pd.get_dummies(df)
 
 
 

pandas/core/reshape.py

@@ -981,25 +981,34 @@ def convert_dummies(data, cat_variables, prefix_sep='_'):
     """
     result = data.drop(cat_variables, axis=1)
     for variable in cat_variables:
-        dummies = get_dummies(data[variable], prefix=variable,
-                              prefix_sep=prefix_sep)
+        dummies = _get_dummies_1d(data[variable], prefix=variable,
+                                  prefix_sep=prefix_sep)
         result = result.join(dummies)
     return result
 
 
-def get_dummies(data, prefix=None, prefix_sep='_', dummy_na=False):
+def get_dummies(data, prefix=None, prefix_sep='_', dummy_na=False,
+                columns=None):
     """
     Convert categorical variable into dummy/indicator variables
 
     Parameters
     ----------
-    data : array-like or Series
-    prefix : string, default None
+    data : array-like, Series, or DataFrame
+    prefix : string, list of strings, or dict of strings, default None
         String to append DataFrame column names
+        Pass a list with length equal to the number of columns
+        when calling get_dummies on a DataFrame. Alternativly, `prefix`
+        can be a dictionary mapping column names to prefixes.
     prefix_sep : string, default '_'
-        If appending prefix, separator/delimiter to use
+        If appending prefix, separator/delimiter to use. Or pass a
+        list or dictionary as with `prefix.`
     dummy_na : bool, default False
         Add a column to indicate NaNs, if False NaNs are ignored.
+    columns : list-like, default None
+        Column names in the DataFrame to be encoded.
+        If `columns` is None then all the columns with
+        `object` or `category` dtype will be converted.
 
     Returns
     -------
@@ -1031,9 +1040,71 @@ def get_dummies(data, prefix=None, prefix_sep='_', dummy_na=False):
     1  0  1    0
     2  0  0    1
 
+    >>> df = DataFrame({'A': ['a', 'b', 'a'], 'B': ['b', 'a', 'c'],
+                        'C': [1, 2, 3]})
+
+    >>> get_dummies(df, prefix=['col1', 'col2']):
+       C  col1_a  col1_b  col2_a  col2_b  col2_c
+    0  1       1       0       0       1       0
+    1  2       0       1       1       0       0
+    2  3       1       0       0       0       1
+
     See also ``Series.str.get_dummies``.
 
     """
+    from pandas.tools.merge import concat
+    from itertools import cycle
+
+    if isinstance(data, DataFrame):
+        # determine columns being encoded
+
+        if columns is None:
+            columns_to_encode = data.select_dtypes(include=['object',
+                'category']).columns
+        else:
+            columns_to_encode = columns
+
+        # validate prefixes and separator to avoid silently dropping cols
+        def check_len(item, name):
+            length_msg = ("Length of '{0}' ({1}) did "
+                           "not match the length of the columns "
+                           "being encoded ({2}).")
+
+            if com.is_list_like(item):
+                if not len(item) == len(columns_to_encode):
+                    raise ValueError(length_msg.format(name, len(item),
+                                     len(columns_to_encode)))
+
+        check_len(prefix, 'prefix')
+        check_len(prefix_sep, 'prefix_sep')
+        if isinstance(prefix, compat.string_types):
+            prefix = cycle([prefix])
+        if isinstance(prefix, dict):
+            prefix = [prefix[col] for col in columns_to_encode]
+
+        if prefix is None:
+            prefix = columns_to_encode
+
+        # validate separators
+        if isinstance(prefix_sep, compat.string_types):
+            prefix_sep = cycle([prefix_sep])
+        elif isinstance(prefix_sep, dict):
+            prefix_sep = [prefix_sep[col] for col in columns_to_encode]
+
+        result = data.drop(columns_to_encode, axis=1)
+        with_dummies = [result]
+        for (col, pre, sep) in zip(columns_to_encode, prefix, prefix_sep):
+
+            dummy = _get_dummies_1d(data[col], prefix=pre,
+                                    prefix_sep=sep, dummy_na=dummy_na)
+            with_dummies.append(dummy)
+        result = concat(with_dummies, axis=1)
+    else:
+        result = _get_dummies_1d(data, prefix, prefix_sep, dummy_na)
+    return result
+
+
+def _get_dummies_1d(data, prefix, prefix_sep='_', dummy_na=False):
     # Series avoids inconsistent NaN handling
     cat = Categorical.from_array(Series(data))
     levels = cat.levels

pandas/tests/test_reshape.py

@@ -149,6 +149,11 @@ def test_multiindex(self):
 
 
 class TestGetDummies(tm.TestCase):
+
+    def setUp(self):
+        self.df = DataFrame({'A': ['a', 'b', 'a'], 'B': ['b', 'b', 'c'],
+                             'C': [1, 2, 3]})
+
     def test_basic(self):
         s_list = list('abc')
         s_series = Series(s_list)
@@ -209,6 +214,114 @@ def test_unicode(self):  # See GH 6885 - get_dummies chokes on unicode values
                         u('letter_%s') % eacute: {0: 0.0, 1: 1.0, 2: 1.0}})
         assert_frame_equal(res, exp)
 
+    def test_dataframe_dummies_all_obj(self):
+        df = self.df[['A', 'B']]
+        result = get_dummies(df)
+        expected = DataFrame({'A_a': [1., 0, 1], 'A_b': [0., 1, 0],
+                              'B_b': [1., 1, 0], 'B_c': [0., 0, 1]})
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_mix_default(self):
+        df = self.df
+        result = get_dummies(df)
+        expected = DataFrame({'C': [1, 2, 3], 'A_a': [1., 0, 1],
+                              'A_b': [0., 1, 0], 'B_b': [1., 1, 0],
+                              'B_c': [0., 0, 1]})
+        expected = expected[['C', 'A_a', 'A_b', 'B_b', 'B_c']]
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_prefix_list(self):
+        prefixes = ['from_A', 'from_B']
+        df = DataFrame({'A': ['a', 'b', 'a'], 'B': ['b', 'b', 'c'],
+                        'C': [1, 2, 3]})
+        result = get_dummies(df, prefix=prefixes)
+        expected = DataFrame({'C': [1, 2, 3], 'from_A_a': [1., 0, 1],
+                              'from_A_b': [0., 1, 0], 'from_B_b': [1., 1, 0],
+                              'from_B_c': [0., 0, 1]})
+        expected = expected[['C', 'from_A_a', 'from_A_b', 'from_B_b',
+                             'from_B_c']]
+        assert_frame_equal(result, expected)
+
+    def test_datafrmae_dummies_prefix_str(self):
+        # not that you should do this...
+        df = self.df
+        result = get_dummies(df, prefix='bad')
+        expected = DataFrame([[1, 1., 0., 1., 0.],
+                              [2, 0., 1., 1., 0.],
+                              [3, 1., 0., 0., 1.]],
+                             columns=['C', 'bad_a', 'bad_b', 'bad_b', 'bad_c'])
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_subset(self):
+        df = self.df
+        result = get_dummies(df, prefix=['from_A'],
+                             columns=['A'])
+        expected = DataFrame({'from_A_a': [1., 0, 1], 'from_A_b': [0., 1, 0],
+                              'B': ['b', 'b', 'c'], 'C': [1, 2, 3]})
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_prefix_sep(self):
+        df = self.df
+        result = get_dummies(df, prefix_sep='..')
+        expected = DataFrame({'C': [1, 2, 3], 'A..a': [1., 0, 1],
+                              'A..b': [0., 1, 0], 'B..b': [1., 1, 0],
+                              'B..c': [0., 0, 1]})
+        expected = expected[['C', 'A..a', 'A..b', 'B..b', 'B..c']]
+        assert_frame_equal(result, expected)
+
+        result = get_dummies(df, prefix_sep=['..', '__'])
+        expected = expected.rename(columns={'B..b': 'B__b', 'B..c': 'B__c'})
+        assert_frame_equal(result, expected)
+
+        result = get_dummies(df, prefix_sep={'A': '..', 'B': '__'})
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_prefix_bad_length(self):
+        with tm.assertRaises(ValueError):
+            get_dummies(self.df, prefix=['too few'])
+
+    def test_dataframe_dummies_prefix_sep_bad_length(self):
+        with tm.assertRaises(ValueError):
+            get_dummies(self.df, prefix_sep=['bad'])
+
+    def test_dataframe_dummies_prefix_dict(self):
+        prefixes = {'A': 'from_A', 'B': 'from_B'}
+        df = DataFrame({'A': ['a', 'b', 'a'], 'B': ['b', 'b', 'c'],
+                        'C': [1, 2, 3]})
+        result = get_dummies(df, prefix=prefixes)
+        expected = DataFrame({'from_A_a': [1., 0, 1], 'from_A_b': [0., 1, 0],
+                              'from_B_b': [1., 1, 0], 'from_B_c': [0., 0, 1],
+                              'C': [1, 2, 3]})
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_with_na(self):
+        df = self.df
+        df.loc[3, :] = [np.nan, np.nan, np.nan]
+        result = get_dummies(df, dummy_na=True)
+        expected = DataFrame({'C': [1, 2, 3, np.nan], 'A_a': [1., 0, 1, 0],
+            'A_b': [0., 1, 0, 0], 'A_nan': [0., 0, 0, 1], 'B_b': [1., 1, 0, 0],
+            'B_c': [0., 0, 1, 0], 'B_nan': [0., 0, 0, 1]})
+        expected = expected[['C', 'A_a', 'A_b', 'A_nan', 'B_b', 'B_c',
+                             'B_nan']]
+        assert_frame_equal(result, expected)
+
+        result = get_dummies(df, dummy_na=False)
+        expected = expected[['C', 'A_a', 'A_b', 'B_b', 'B_c']]
+        assert_frame_equal(result, expected)
+
+    def test_dataframe_dummies_with_categorical(self):
+        df = self.df
+        df['cat'] = pd.Categorical(['x', 'y', 'y'])
+        result = get_dummies(df)
+        expected = DataFrame({'C': [1, 2, 3], 'A_a': [1., 0, 1],
+                              'A_b': [0., 1, 0], 'B_b': [1., 1, 0],
+                              'B_c': [0., 0, 1], 'cat_x': [1., 0, 0],
+                              'cat_y': [0., 1, 1]})
+        expected = expected[['C', 'A_a', 'A_b', 'B_b', 'B_c',
+                             'cat_x', 'cat_y']]
+        assert_frame_equal(result, expected)
+
+
 class TestConvertDummies(tm.TestCase):
     def test_convert_dummies(self):
         df = DataFrame({'A': ['foo', 'bar', 'foo', 'bar',