Merge pull request pydata#90 from njsmith/fix-89

njsmith · web-flow · commit e877b74a5ce0 · 2016-10-25T12:58:04.000-07:00
Allow degenerate linear constraints
diff --git a/patsy/constraint.py b/patsy/constraint.py
@@ -58,8 +58,6 @@ def __init__(self, variable_names, coefs, constants=None):
             raise ValueError("must have at least one row in constraint matrix")
         if self.coefs.shape[0] != self.constants.shape[0]:
             raise ValueError("shape mismatch between coefs and constants")
-        if np.any(np.all(self.coefs == 0, axis=1)):
-            raise ValueError("can't test a constant constraint")
 
     __repr__ = repr_pretty_delegate
     def _repr_pretty_(self, p, cycle):
@@ -102,12 +100,19 @@ def test_LinearConstraint():
     assert lc.coefs.dtype == np.dtype(float)
     assert lc.constants.dtype == np.dtype(float)
 
+
+    # statsmodels wants to be able to create degenerate constraints like this,
+    # see:
+    #     https://github.com/pydata/patsy/issues/89
+    # We used to forbid it, but I guess it's harmless, so why not.
+    lc = LinearConstraint(["a"], [[0]])
+    assert_equal(lc.coefs, [[0]])
+
     from nose.tools import assert_raises
     assert_raises(ValueError, LinearConstraint, ["a"], [[1, 2]])
     assert_raises(ValueError, LinearConstraint, ["a"], [[[1]]])
     assert_raises(ValueError, LinearConstraint, ["a"], [[1, 2]], [3, 4])
     assert_raises(ValueError, LinearConstraint, ["a", "b"], [[1, 2]], [3, 4])
-    assert_raises(ValueError, LinearConstraint, ["a"], [[0]])
     assert_raises(ValueError, LinearConstraint, ["a"], [[1]], [[]])
     assert_raises(ValueError, LinearConstraint, ["a", "b"], [])
     assert_raises(ValueError, LinearConstraint, ["a", "b"],
