ENH: add `invert` parameter to numpy.in1d().

2 files changed, 19 insertions, 3 deletions

diff --git a/numpy/ma/extras.py b/numpy/ma/extras.py
index a809db53c..861fefad0 100644
--- a/numpy/ma/extras.py
+++ b/numpy/ma/extras.py
@@ -1121,7 +1121,7 @@ def setxor1d(ar1, ar2, assume_unique=False):
     flag2 = (flag[1:] == flag[:-1])
     return aux[flag2]
 
-def in1d(ar1, ar2, assume_unique=False):
+def in1d(ar1, ar2, assume_unique=False, invert=False):
     """
     Test whether each element of an array is also present in a second
     array.
@@ -1147,8 +1147,11 @@ def in1d(ar1, ar2, assume_unique=False):
     # the values from the second array.
     order = ar.argsort(kind='mergesort')
     sar = ar[order]
-    equal_adj = (sar[1:] == sar[:-1])
-    flag = ma.concatenate((equal_adj, [False]))
+    if invert:
+        bool_ar = (sar[1:] != sar[:-1])
+    else:
+        bool_ar = (sar[1:] == sar[:-1])
+    flag = ma.concatenate((bool_ar, [invert]))
     indx = order.argsort(kind='mergesort')[:len(ar1)]
 
     if assume_unique:
diff --git a/numpy/ma/tests/test_extras.py b/numpy/ma/tests/test_extras.py
index b6643fc4d..d9f94a01f 100644
--- a/numpy/ma/tests/test_extras.py
+++ b/numpy/ma/tests/test_extras.py
@@ -810,6 +810,19 @@ class TestArraySetOps(TestCase):
         assert_array_equal([], in1d([], []))
 
 
+    def test_in1d_invert(self):
+        "Test in1d's invert parameter"
+        a = array([1, 2, 5, 7, -1], mask=[0, 0, 0, 0, 1])
+        b = array([1, 2, 3, 4, 5, -1], mask=[0, 0, 0, 0, 0, 1])
+        assert_equal(np.invert(in1d(a, b)), in1d(a, b, invert=True))
+
+        a = array([5, 5, 2, 1, -1], mask=[0, 0, 0, 0, 1])
+        b = array([1, 5, -1], mask=[0, 0, 1])
+        assert_equal(np.invert(in1d(a, b)), in1d(a, b, invert=True))
+
+        assert_array_equal([], in1d([], [], invert=True))
+
+
     def test_union1d(self):
         "Test union1d"
         a = array([1, 2, 5, 7, 5, -1], mask=[0, 0, 0, 0, 0, 1])