Add where function

docs/source/xarray.rst

@@ -126,6 +126,7 @@ where ``condition`` is falsy, and it does not evaluate ``b`` where ``condition``
 |            Python 3 - xarray                  |                C++ 14 - xframe                |
 +===============================================+===============================================+
 | ``xr.where(a > 5, a, b)``                     | ``xf::where(a > 5, a, b)``                    |
+| ``xr.where(a > 5, 100, a)``                   | ``xf::where(a > 5, 100, a)``                  |
 +-----------------------------------------------+-----------------------------------------------+
 | ``np.any(a)``                                 | ``xf::any(a)``                                |
 +-----------------------------------------------+-----------------------------------------------+
@@ -251,4 +252,3 @@ xframe universal functions are provided for a large set number of mathematical f
 +-----------------------------------------------+-----------------------------------------------+
 | ``scipy.special.gammaln(a)``                  | ``xf::lgamma(a)``                             |
 +-----------------------------------------------+-----------------------------------------------+
-

include/xframe/xaxis_math.hpp

@@ -114,6 +114,8 @@ namespace xf
     // Needs a fix in xtensor
     /*using xt::isclose;
     using xt::allclose;*/
+
+    using xt::where;
 }
 
 #endif

test/test_xvariable_math.cpp

@@ -7,7 +7,12 @@
 ****************************************************************************/
 
 #include <algorithm>
+
 #include "gtest/gtest.h"
+
+#include "xtensor/xarray.hpp"
+#include "xtensor/xoptional_assembly.hpp"
+
 #include "test_fixture.hpp"
 
 namespace xf
@@ -278,7 +283,7 @@ namespace xf
 
         EXPECT_EQ(fma(sa, sb, a.select(sel)), xf::fma(sa, sb, a).select(sel));
     }
-    
+
     TEST(xvariable_math, fmax)
     {
         variable_type a = make_test_variable();
@@ -657,11 +662,34 @@ namespace xf
         EXPECT_EQ(isnan(a.select(sel)), xf::isnan(a).select(sel));
     }
 
+    TEST(xvariable_math, where)
+    {
+        auto missing = xtl::missing<double>();
+        using data_type = xt::xoptional_assembly<xt::xarray<double>, xt::xarray<bool>>;
+
+        variable_type a = make_test_variable();
+        variable_type b = make_test_variable2();
+
+        variable_type res = where(a < 6, b, a);
+
+        data_type expected = {{{     1.,      2., missing},
+                               {missing, missing, missing}},
+                              {{     7.,      7.,      7.},
+                               {     9.,      9.,      9.}}};
+        EXPECT_EQ(res.data(), expected);
+
+        variable_type res2 = where(a < 6, 0., a);
+        data_type expected2 = {{      0,   0, missing},
+                               {missing,   0,       6},
+                               {      7,   8,       9}};
+        EXPECT_EQ(res2.data(), expected2);
+    }
+
     // Needs a fix in xtensor
     /*TEST(xvariable_math, isclose)
     {
         variable_type a = make_test_variable();
         dict_type sel = make_selector_aa();
         EXPECT_TRUE(isclose(a, a).select(sel));
     }*/
-}
+}