[GitHub] [arrow] mrkn commented on a diff in pull request #13377: ARROW-14518: [Ruby] Add support for Arrow::Array.new([BigDecimal])

[GitBox <gi...@apache.org>]

mrkn commented on code in PR #13377:
URL: https://github.com/apache/arrow/pull/13377#discussion_r898144157


##########
ruby/red-arrow/lib/arrow/array-builder.rb:
##########
@@ -121,15 +126,28 @@ def detect_builder_info(value, builder_info)
             detected: true,
           }
         when BigDecimal
-          if value.to_arrow.is_a?(Decimal128)
-            {
-              builder: Decimal128ArrayBuilder.new,
-            }
-          else
+          builder_info ||= {}
+          if builder_info[:builder]
             {
-              builder: Decimal256ArrayBuilder.new,
+              builder: StringArrayBuilder.new,
               detected: true,
             }
+          else
+            precision = [builder_info[:precision] || 0, value.precision].max
+            scale = [builder_info[:scale] || 0, value.scale].max

Review Comment:
   These 2 lines don't permit overwriting the value's precision and the scale with smaller values by specifying the precision and the scale in `builder_info`.  Is it intentional?



##########
ruby/red-arrow/test/test-array-builder.rb:
##########
@@ -68,6 +68,56 @@ def assert_build(builder_class, raw_array)
                      ])
       end
 
+      test("decimal + string") do
+        raw_array = [BigDecimal("10.1"), "10.1"]
+        array = Arrow::ArrayBuilder.build(raw_array)
+        assert_equal(raw_array.collect(&:to_s), array.to_a)
+      end
+
+      test("decimal128") do
+        values = [
+          BigDecimal("10.1"),
+          BigDecimal("1.11"),
+          BigDecimal("1"),
+        ]
+        array = Arrow::Array.new(values)
+        data_type = Arrow::Decimal128DataType.new(3, 2)
+        assert_equal({
+                       data_type: data_type,
+                       values: [
+                         BigDecimal("10.1"),
+                         BigDecimal("1.11"),
+                         BigDecimal("1"),
+                       ],
+                     },
+                     {
+                       data_type: array.value_data_type,
+                       values: array.to_a,
+                     })
+      end
+
+      test("decimal256") do
+        values = [
+          BigDecimal("1" * 40 + ".1"),
+          BigDecimal("1" * 38 + ".11"),
+          BigDecimal("1" * 37),
+        ]
+        array = Arrow::Array.new(values)
+        data_type = Arrow::Decimal256DataType.new(41, 2)
+        assert_equal({
+                       data_type: data_type,
+                       values: [
+                         BigDecimal("1" * 40 + ".1"),
+                         BigDecimal("1" * 38 + ".11"),
+                         BigDecimal("1" * 37),
+                       ],
+                     },
+                     {
+                       data_type: array.value_data_type,
+                       values: array.to_a,
+                     })
+      end
+

Review Comment:
   Is it unnecessary to test with `BigDecimal::NAN` and `BigDecimal::INFINITY`?



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