[numpy] adds sigmaclip_mask

numpy.py

@@ -87,3 +87,18 @@ def intersect2d(A, B, *args, **kwargs):
         c = C
     c = c.view(A.dtype).reshape(-1, ncols)
     return C
+
+
+def sigmaclip_mask(arr, low=4.0, high=4.0):
+    delta = 1
+    arr = np.array(arr)
+    mask = np.ones_like(arr, dtype=bool)
+    while delta:
+        arr_std = arr[mask].std()
+        arr_mean = arr[mask].mean()
+        good = np.sum(mask)
+        critlower = arr_mean - arr_std * low
+        critupper = arr_mean + arr_std * high
+        mask = mask & (arr >= critlower) & (arr <= critupper)
+        delta = good - np.sum(mask)
+    return ~mask