ENH: Add support for datetimes to histograms

Currently only supported for explicit bins

2 files changed, 36 insertions, 9 deletions

diff --git a/numpy/lib/histograms.py b/numpy/lib/histograms.py
index ccae9de22..a19ff07d8 100644
--- a/numpy/lib/histograms.py
+++ b/numpy/lib/histograms.py
@@ -217,23 +217,25 @@ def _get_outer_edges(a, range):
     Determine the outer bin edges to use, from either the data or the range
     argument
     """
-    if range is None:
-        if a.size == 0:
-            # handle empty arrays. Can't determine range, so use 0-1.
-            first_edge, last_edge = 0.0, 1.0
-        else:
-            first_edge, last_edge = a.min() + 0.0, a.max() + 0.0
+    if range is not None:
+        first_edge, last_edge = range
+    elif a.size == 0:
+        # handle empty arrays. Can't determine range, so use 0-1.
+        first_edge, last_edge = 0, 1
     else:
-        first_edge, last_edge = [mi + 0.0 for mi in range]
+        first_edge, last_edge = a.min(), a.max()
+
     if first_edge > last_edge:
         raise ValueError(
             'max must be larger than min in range parameter.')
     if not (np.isfinite(first_edge) and np.isfinite(last_edge)):
         raise ValueError(
             'range parameter must be finite.')
+
+    # expand empty range to avoid divide by zero
     if first_edge == last_edge:
-        first_edge -= 0.5
-        last_edge += 0.5
+        first_edge = first_edge - 0.5
+        last_edge = last_edge + 0.5
 
     return first_edge, last_edge
 
diff --git a/numpy/lib/tests/test_histograms.py b/numpy/lib/tests/test_histograms.py
index 0986ad16b..58547dc17 100644
--- a/numpy/lib/tests/test_histograms.py
+++ b/numpy/lib/tests/test_histograms.py
@@ -274,6 +274,31 @@ class TestHistogram(object):
             h, b = histogram(all_nan, bins=[0, 1])
             assert_equal(h.sum(), 0)  # nan is not counted
 
+    def test_datetime(self):
+        begin = np.datetime64('2000-01-01', 'D')
+        offsets = np.array([0, 0, 1, 1, 2, 3, 5, 10, 20])
+        bins = np.array([0, 2, 7, 20])
+        dates = begin + offsets
+        date_bins = begin + bins
+
+        td = np.dtype('timedelta64[D]')
+
+        # Results should be the same for integer offsets or datetime values.
+        # For now, only explicit bins are supported, since linspace does not
+        # work on datetimes or timedeltas
+        d_count, d_edge = histogram(dates, bins=date_bins)
+        t_count, t_edge = histogram(offsets.astype(td), bins=bins.astype(td))
+        i_count, i_edge = histogram(offsets, bins=bins)
+
+        assert_equal(d_count, i_count)
+        assert_equal(t_count, i_count)
+
+        assert_equal((d_edge - begin).astype(int), i_edge)
+        assert_equal(t_edge.astype(int), i_edge)
+
+        assert_equal(d_edge.dtype, dates.dtype)
+        assert_equal(t_edge.dtype, td)
+
 
 class TestHistogramOptimBinNums(object):
     """