BUG: COMPAT:0.18 added scipy version check

closes #12887
closes #13007

Author: Jason Wolosonovich

doc/source/whatsnew/v0.18.1.txt

@@ -512,6 +512,7 @@ Other API changes
 - Provide a proper ``__name__`` and ``__qualname__`` attributes for generic functions (:issue:`12021`)
 - ``pd.concat(ignore_index=True)`` now uses ``RangeIndex`` as default (:issue:`12695`)
 - ``pd.merge()`` and ``DataFrame.join()`` will show a ``UserWarning`` when merging/joining a single- with a multi-leveled dataframe (:issue:`9455`, :issue:`12219`)
+- Compat with SciPy > 0.17 for deprecated ``piecewise_polynomial`` interpolation method (:issue:`12887`)
 
 .. _whatsnew_0181.deprecations:
 

pandas/core/generic.py

@@ -3452,8 +3452,8 @@ def replace(self, to_replace=None, value=None, inplace=False, limit=None,
         ----------
         method : {'linear', 'time', 'index', 'values', 'nearest', 'zero',
                   'slinear', 'quadratic', 'cubic', 'barycentric', 'krogh',
-                  'polynomial', 'spline' 'piecewise_polynomial', 'pchip',
-                  'akima'}
+                  'polynomial', 'spline', 'piecewise_polynomial',
+                  'from_derivatives', 'pchip', 'akima'}
 
             * 'linear': ignore the index and treat the values as equally
               spaced. This is the only method supported on MultiIndexes.
@@ -3473,9 +3473,15 @@ def replace(self, to_replace=None, value=None, inplace=False, limit=None,
               the scipy documentation for more on their behavior
               `here <http://docs.scipy.org/doc/scipy/reference/interpolate.html#univariate-interpolation>`__  # noqa
               `and here <http://docs.scipy.org/doc/scipy/reference/tutorial/interpolate.html>`__  # noqa
+            * 'from_derivatives' refers to BPoly.from_derivatives which
+              replaces 'piecewise_polynomial' interpolation method in scipy 0.18
 
             .. versionadded:: 0.18.1
+
                Added support for the 'akima' method
+               Added interpolate method 'from_derivatives' which replaces
+               'piecewise_polynomial' in scipy 0.18; backwards-compatible with
+               scipy < 0.18
 
         axis : {0, 1}, default 0
             * 0: fill column-by-column

pandas/core/missing.py

@@ -3,6 +3,7 @@
 """
 
 import numpy as np
+from distutils.version import LooseVersion
 
 import pandas.core.common as com
 import pandas.algos as algos
@@ -85,13 +86,15 @@ def clean_interp_method(method, **kwargs):
     order = kwargs.get('order')
     valid = ['linear', 'time', 'index', 'values', 'nearest', 'zero', 'slinear',
              'quadratic', 'cubic', 'barycentric', 'polynomial', 'krogh',
-             'piecewise_polynomial', 'pchip', 'akima', 'spline']
+             'piecewise_polynomial', 'pchip', 'akima', 'spline',
+             'from_derivatives']
     if method in ('spline', 'polynomial') and order is None:
         raise ValueError("You must specify the order of the spline or "
                          "polynomial.")
     if method not in valid:
         raise ValueError("method must be one of {0}."
                          "Got '{1}' instead.".format(valid, method))
+
     return method
 
 
@@ -191,7 +194,8 @@ def _interp_limit(invalid, fw_limit, bw_limit):
 
     sp_methods = ['nearest', 'zero', 'slinear', 'quadratic', 'cubic',
                   'barycentric', 'krogh', 'spline', 'polynomial',
-                  'piecewise_polynomial', 'pchip', 'akima']
+                  'from_derivatives', 'piecewise_polynomial', 'pchip', 'akima']
+
     if method in sp_methods:
         inds = np.asarray(xvalues)
         # hack for DatetimeIndex, #1646
@@ -228,7 +232,8 @@ def _interpolate_scipy_wrapper(x, y, new_x, method, fill_value=None,
     alt_methods = {
         'barycentric': interpolate.barycentric_interpolate,
         'krogh': interpolate.krogh_interpolate,
-        'piecewise_polynomial': interpolate.piecewise_polynomial_interpolate,
+        'from_derivatives': _from_derivatives,
+        'piecewise_polynomial': _from_derivatives,
     }
 
     if getattr(x, 'is_all_dates', False):
@@ -277,6 +282,60 @@ def _interpolate_scipy_wrapper(x, y, new_x, method, fill_value=None,
     return new_y
 
 
+def _from_derivatives(xi, yi, x, order=None, der=0, extrapolate=False):
+    """
+    Convenience function for interpolate.BPoly.from_derivatives
+
+    Construct a piecewise polynomial in the Bernstein basis, compatible
+    with the specified values and derivatives at breakpoints.
+
+    Parameters
+    ----------
+    xi : array_like
+        sorted 1D array of x-coordinates
+    yi : array_like or list of array-likes
+        yi[i][j] is the j-th derivative known at xi[i]
+    orders : None or int or array_like of ints. Default: None.
+        Specifies the degree of local polynomials. If not None, some
+        derivatives are ignored.
+    der : int or list
+        How many derivatives to extract; None for all potentially nonzero
+        derivatives (that is a number equal to the number of points), or a
+        list of derivatives to extract. This numberincludes the function
+        value as 0th derivative.
+     extrapolate : bool, optional
+        Whether to extrapolate to ouf-of-bounds points based on first and last
+        intervals, or to return NaNs. Default: True.
+
+    See Also
+    --------
+    scipy.interpolate.BPoly.from_derivatives
+
+    Returns
+    -------
+    y : scalar or array_like
+        The result, of length R or length M or M by R,
+
+    """
+    import scipy
+    from scipy import interpolate
+
+    if LooseVersion(scipy.__version__) < '0.18.0':
+        try:
+            method = interpolate.piecewise_polynomial_interpolate
+            return method(xi, yi.reshape(-1, 1), x,
+                          orders=order, der=der)
+        except AttributeError:
+            pass
+
+    # return the method for compat with scipy version & backwards compat
+    method = interpolate.BPoly.from_derivatives
+    m = method(xi, yi.reshape(-1, 1),
+               orders=order, extrapolate=extrapolate)
+
+    return m(x)
+
+
 def _akima_interpolate(xi, yi, x, der=0, axis=0):
     """
     Convenience function for akima interpolation.

pandas/tests/series/test_missing.py

@@ -533,6 +533,36 @@ def test_interpolate_akima(self):
         interp_s = ser.reindex(new_index).interpolate(method='akima')
         assert_series_equal(interp_s[1:3], expected)
 
+    def test_interpolate_piecewise_polynomial(self):
+        tm._skip_if_no_scipy()
+
+        ser = Series([10, 11, 12, 13])
+
+        expected = Series([11.00, 11.25, 11.50, 11.75,
+                           12.00, 12.25, 12.50, 12.75, 13.00],
+                          index=Index([1.0, 1.25, 1.5, 1.75,
+                                       2.0, 2.25, 2.5, 2.75, 3.0]))
+        # interpolate at new_index
+        new_index = ser.index.union(Index([1.25, 1.5, 1.75, 2.25, 2.5, 2.75]))
+        interp_s = ser.reindex(new_index).interpolate(
+            method='piecewise_polynomial')
+        assert_series_equal(interp_s[1:3], expected)
+
+    def test_interpolate_from_derivatives(self):
+        tm._skip_if_no_scipy()
+
+        ser = Series([10, 11, 12, 13])
+
+        expected = Series([11.00, 11.25, 11.50, 11.75,
+                           12.00, 12.25, 12.50, 12.75, 13.00],
+                          index=Index([1.0, 1.25, 1.5, 1.75,
+                                       2.0, 2.25, 2.5, 2.75, 3.0]))
+        # interpolate at new_index
+        new_index = ser.index.union(Index([1.25, 1.5, 1.75, 2.25, 2.5, 2.75]))
+        interp_s = ser.reindex(new_index).interpolate(
+            method='from_derivatives')
+        assert_series_equal(interp_s[1:3], expected)
+
     def test_interpolate_corners(self):
         s = Series([np.nan, np.nan])
         assert_series_equal(s.interpolate(), s)