Fix mapping discrete column to integer values

fixes has2k1#108

Author: has2k1

doc/changelog.rst

@@ -48,6 +48,9 @@ Bug Fixes
   ignored when determining the axis titles. Now, the ``name`` parameter
   is specified, it is used as the title. (:issue:`105`)
 
+- Fixed bug in discrete scales where a column could not be mapped
+  to integer values. (:issue:`108`)
+
 v0.3.0
 ------
 *(2017-11-08)*

plotnine/scales/scale.py

@@ -284,7 +284,9 @@ def map(self, x, limits=None):
         else:
             pal = np.asarray(pal)
             pal_match = pal[match(x, limits)]
-            pal_match[pd.isnull(pal_match)] = self.na_value
+            bool_idx = pd.isnull(pal_match)
+            if np.any(bool_idx):
+                pal_match[bool_idx] = self.na_value
         return pal_match
 
     def break_info(self, range=None):

plotnine/tests/test_scale_internals.py

@@ -3,6 +3,7 @@
 from datetime import datetime
 
 import numpy as np
+import numpy.testing as npt
 import pandas as pd
 import pytest
 import six
@@ -22,6 +23,7 @@
                                         scale_size_continuous,
                                         scale_size_area,
                                         scale_size_radius)
+from plotnine.scales.scale_manual import _scale_manual
 from plotnine.scales.scales import make_scale
 from plotnine.exceptions import PlotnineError
 
@@ -378,3 +380,21 @@ def test_scale_without_a_mapping():
          + scale_color.scale_color_continuous())
     with pytest.warns(UserWarning):
         p.draw_test()
+
+
+def scale_scale_discrete_mapping_nulls():
+    a = np.array([1, 2, 3], dtype=object)
+
+    sc = _scale_manual([1, 2, 3, 4, 5])
+    sc.train(a)
+    res = sc.map([1, 2, 3])
+    expected = np.array([1, 2, 3])
+    npt.assert_array_equal(res, expected)
+
+    sc = _scale_manual([1, None, 3, 4, 5])
+    sc.train(a)
+    res = sc.map([1, 2, 3])
+    expected = np.array([1, np.nan, 3])
+    assert res[0] == expected[0]
+    assert res[1] is expected[1]
+    assert res[2] == expected[2]