Imporove Arrow::ArrayStatistics#null_count

Author: kou

ruby/red-arrow/lib/arrow/array-statistics.rb

@@ -17,6 +17,18 @@
 
 module Arrow
   class ArrayStatistics
+    if method_defined?(:null_count_exact)
+      alias_method :null_count_raw, :null_count
+      def null_count
+        return nil unless has_null_count?
+        if null_count_exact?
+          null_count_exact
+        else
+          null_count_approximate
+        end
+      end
+    end
+
     if method_defined?(:distinct_count_exact)
       alias_method :distinct_count_raw, :distinct_count
       def distinct_count

ruby/red-parquet/test/test-array-statistics.rb

@@ -27,6 +27,16 @@ def setup
     @statistics = loaded_table[:int64].data.chunks[0].statistics
   end
 
+  def test_null_count
+    assert do
+      @statistics.has_null_count?
+    end
+    assert do
+      @statistics.null_count_exact?
+    end
+    assert_equal(1, @statistics.null_count)
+  end
+
   def test_distinct_count
     assert do
       not @statistics.has_distinct_count?