ARROW-4859: [GLib] Add garrow_numeric_array_mean()

c_glib/arrow-glib/basic-array.cpp

@@ -939,6 +939,33 @@ garrow_numeric_array_class_init(GArrowNumericArrayClass *klass)
 {
 }
 
+/**
+ * garrow_numeric_array_mean:
+ * @array: A #GArrowNumericArray.
+ * @error: (nullable): Return location for a #GError or %NULL.
+ *
+ * Returns: The value of the computed mean.
+ *
+ * Since: 0.13.0
+ */
+gdouble
+garrow_numeric_array_mean(GArrowNumericArray *array,
+                          GError **error)
+{
+  auto arrow_array = garrow_array_get_raw(GARROW_ARRAY(array));
+  auto memory_pool = arrow::default_memory_pool();
+  arrow::compute::FunctionContext context(memory_pool);
+  arrow::compute::Datum mean_datum;
+  auto status = arrow::compute::Mean(&context, arrow_array, &mean_datum);
+  if (garrow_error_check(error, status, "[numeric-array][mean]")) {
+    using ScalarType = typename arrow::TypeTraits<arrow::DoubleType>::ScalarType;
+    auto arrow_numeric_scalar = std::dynamic_pointer_cast<ScalarType>(mean_datum.scalar());
+    return arrow_numeric_scalar->value;
+  } else {
+    return 0.0;
+  }
+}
+
 
 G_DEFINE_TYPE(GArrowInt8Array,
               garrow_int8_array,

c_glib/arrow-glib/basic-array.h

@@ -212,6 +212,10 @@ struct _GArrowNumericArrayClass
   GArrowPrimitiveArrayClass parent_class;
 };
 
+GARROW_AVAILABLE_IN_0_13
+gdouble garrow_numeric_array_mean(GArrowNumericArray *array,
+                                  GError **error);
+
 #define GARROW_TYPE_INT8_ARRAY (garrow_int8_array_get_type())
 G_DECLARE_DERIVABLE_TYPE(GArrowInt8Array,
                          garrow_int8_array,

c_glib/test/test-numeric-array.rb

@@ -0,0 +1,26 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+class TestNumericArray < Test::Unit::TestCase
+  include Helper::Buildable
+
+  def test_mean
+    array = build_double_array([1.1, 2.2, nil])
+    assert_in_delta(array.values.sum / 2,
+                    array.mean)
+  end
+end

cpp/src/arrow/compute/api.h

@@ -24,5 +24,6 @@
 #include "arrow/compute/kernels/boolean.h"  // IWYU pragma: export
 #include "arrow/compute/kernels/cast.h"     // IWYU pragma: export
 #include "arrow/compute/kernels/hash.h"     // IWYU pragma: export
+#include "arrow/compute/kernels/mean.h"     // IWYU pragma: export
 
 #endif  // ARROW_COMPUTE_API_H