fix floating point precision in floatyear_to_date (#1747)

* fix floating point precision in floatyear_to_date

* small optimization, more tests

* fix test

* simplify type checking in floatyear_to_date

oggm/tests/test_utils.py

@@ -123,6 +123,16 @@ def test_floatyear_to_date(self):
         r = utils.floatyear_to_date(yr)
         assert r == (1998, 2)
 
+        # tests for floating point precision
+        yr = 1 + 1/12 - 1/12
+        r = utils.floatyear_to_date(yr)
+        assert r == (1, 1)
+
+        for i in range(12):
+            yr = 2000
+            r = utils.floatyear_to_date(yr + i / 12)
+            assert r == (yr, i + 1)
+
     def test_date_to_floatyear(self):
 
         r = utils.date_to_floatyear(0, 1)

oggm/utils/_funcs.py

@@ -690,6 +690,19 @@ def floatyear_to_date(yr):
     if isinstance(yr, xr.DataArray):
         yr = yr.values
 
+    # Ensure yr is a np.array, even for scalar values
+    yr = np.atleast_1d(yr).astype(np.float64)
+
+    # check if year is inside machine precision to next higher int
+    yr_ceil = np.ceil(yr)
+    yr = np.where(np.isclose(yr,
+                             yr_ceil,
+                             rtol=np.finfo(np.float64).eps,
+                             atol=0
+                             ),
+                  yr_ceil,
+                  yr)
+
     out_y, remainder = np.divmod(yr, 1)
     out_y = out_y.astype(int)
 
@@ -700,7 +713,7 @@ def floatyear_to_date(yr):
                                 np.round(month_exact),
                                 np.floor(month_exact)).astype(int))
 
-    if (isinstance(yr, list) or isinstance(yr, np.ndarray)) and len(yr) == 1:
+    if yr.size == 1:
         out_y = out_y.item()
         out_m = out_m.item()