Filter condition is not broadcasted

include/xtensor/xindex_view.hpp

@@ -780,6 +780,29 @@ namespace xt
         return view_type(std::forward<E>(e), std::move(indices));
     }
 
+	/**
+     * @brief creates a view into \a e filtered by \a condition.
+     *
+     * Returns an xt::view (2D view) with the rows selected where \a condition evaluates to \em true.
+     *
+     * @param e the underlying xexpression
+     * @param condition xexpression with shape of \a e which selects rows
+     *
+     * \code{.cpp}
+	 * xarray<int> a = { { 0, 1, 2, 3 }, { 4, 5, 6, 7 }, { 8, 9, 10, 11 } };
+	 * auto filter = xt::filter_rows(a, xt::view(a, xt::all(), 0) > 4);
+	 * std::cout << filter << std:endl; // { {8, 9, 10, 11} }
+     * \endcode
+     */
+	template <class E, class O>
+	inline auto filter_rows(E&& e, O&& condition) noexcept
+	{
+		auto row_indices = rowwhere(std::forward<O>(condition));
+		return view(e, keep(row_indices), all());
+	}
+
+
+
     /**
      * @brief creates a filtration of \c e filtered by \a condition.
      *

include/xtensor/xoperation.hpp

@@ -890,6 +890,37 @@ namespace xt
         return indices;
     }
 
+	/**
+     * @ingroup logical_operators
+     * @brief return vector of row indices where arr is not zero
+     *
+     * @param arr input array
+     * @return vector of size_types where arr is not equal to zero
+     */
+	template <class T>
+    inline auto rowwhere(const T& arr)
+    {
+        auto shape = arr.shape();
+        using index_type = xindex_type_t<typename T::shape_type>;
+        using size_type = typename T::size_type;
+
+        auto idx = xtl::make_sequence<index_type>(arr.dimension(), 0);
+        std::vector<size_type> indices;
+
+        size_type total_size = compute_size(shape);
+        for (size_type i = 0; i < total_size; i++, detail::next_idx(shape, idx))
+        {
+            if (arr.element(std::begin(idx), std::end(idx)))
+            {
+                indices.push_back(i);
+            }
+        }
+
+        return indices;
+    }
+
+
+
     /**
     * @ingroup logical_operators
     * @brief Any

test/test_xindex_view.cpp

@@ -153,6 +153,15 @@ namespace xt
         EXPECT_EQ(expected, a);
     }
 
+	TEST(xindex_view, filter_row)
+    {
+		xarray<int> a = { { 0, 1, 2, 3 },{ 4, 5, 6, 7 },{ 8, 9, 10, 11 } };
+		xarray<int> res = { {8, 9, 10, 11} };
+		auto filter = filter_rows(a, view(a, all(), 0) > 4);
+
+        EXPECT_EQ(filter, res);
+    }
+
     TEST(xindex_view, const_adapt_filter)
     {
         const std::vector<double> av({1,2,3,4,5,6});