Merge pull request #217 from bashtage/add-cubic-regression-spline

ENH: Add cubic regression spline

Author: matthewwardrop

docsite/docs/changelog.md

@@ -3,6 +3,14 @@ For changes since the latest tagged release, please refer to the
 
 ---
 
+## 1.1.0 (Unreleased)
+
+** Enhancements **
+
+* Added cubic spline support for cyclic (`cc`) and natural (`cr`). See
+ `formulaic.materializers.transforms.cubic_spline.cubic_spline` for 
+  more details. 
+
 ## 1.0.2 (12 July 2024)
 
 **Bugfixes and cleanups:**

docsite/docs/guides/grammar.md

@@ -68,8 +68,9 @@ that have *not* been implemented by `formulaic` are explicitly noted also.
 | `lag(...[, <k>])` | Generate lagging or leading columns (useful for datasets collected at regular intervals). | ✓ | ✗ | ✓ |
 | `poly(...)` | Generates a polynomial basis, allowing non-linear fits. | ✓ | ✗ | ✓ |
 | `bs(...)` | Generates a B-Spline basis, allowing non-linear fits. | ✓ | ✓ | ✓ |
-| `cr(...)` | Generates a natural cubic spline basis, allowing non-linear fits. | ✗ | ✓ | ✓ |
-| `cc(...)` | Generates a cyclic cubic spline basis, allowing non-linear fits. | ✗ | ✓ | ✓ |
+| `cs(...)` | Generates a natural cubic spline basis, allowing non-linear fits. | ✓ | ✓ | ✓ |
+| `cr(...)` | Alias for `cs` above. | ✓ | ✗ | ✓ |
+| `cc(...)` | Generates a cyclic cubic spline basis, allowing non-linear fits. | ✓ | ✓ | ✓ |
 | `te(...)` | Generates a tensor product smooth. | ✗ | ✓ | ✓ |
 | `hashed(...)` | Categorically encode a deterministic hash of a column. | ✓ | ✗ | ✗ |
 | ...       | Others? Contributions welcome!     | ? | ? | ? |

docsite/docs/guides/splines.ipynb

@@ -4,6 +4,7 @@
 
 from .basis_spline import basis_spline
 from .contrasts import C, ContrastsRegistry, encode_contrasts
+from .cubic_spline import cyclic_cubic_spline, natural_cubic_spline
 from .hashed import hashed
 from .identity import identity
 from .lag import lag
@@ -13,6 +14,9 @@
 
 __all__ = [
     "basis_spline",
+    "cubic_spline",
+    "cyclic_cubic_spline",
+    "natural_cubic_spline",
     "identity",
     "C",
     "encode_contrasts",
@@ -36,6 +40,9 @@
     "exp2": numpy.exp2,
     # Bespoke transforms
     "bs": basis_spline,
+    "cc": cyclic_cubic_spline,
+    "cr": natural_cubic_spline,
+    "cs": natural_cubic_spline,
     "center": center,
     "lag": lag,
     "poly": poly,