GH-37978: [C++] Add support for specifying custom Array element delimiter to arrow::PrettyPrintOptions

cpp/src/arrow/pretty_print.cc

@@ -151,22 +151,22 @@ class ArrayPrinter : public PrettyPrinter {
         IndentAfterNewline();
         (*sink_) << "...";
         if (!is_last && options_.skip_new_lines) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_element_delimiter;
         }
         i = array.length() - window - 1;
       } else if (array.IsNull(i)) {
         IndentAfterNewline();
         (*sink_) << options_.null_rep;
         if (!is_last) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_element_delimiter;
         }
       } else {
         if (indent_non_null_values) {
           IndentAfterNewline();
         }
         RETURN_NOT_OK(func(i));
         if (!is_last) {
-          (*sink_) << ",";
+          (*sink_) << options_.array_element_delimiter;
         }
       }
       Newline();

cpp/src/arrow/pretty_print.h

@@ -77,6 +77,9 @@ struct PrettyPrintOptions {
 
   /// If true, display schema metadata when pretty-printing a Schema
   bool show_schema_metadata = true;
+
+  /// Delimiter for separating individual elements of an Array (e.g. ",")
+  std::string array_element_delimiter = ",";
 };
 
 /// \brief Print human-readable representation of RecordBatch

cpp/src/arrow/pretty_print_test.cc

@@ -200,6 +200,53 @@ TEST_F(TestPrettyPrint, PrimitiveTypeNoNewlines) {
   CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
 }
 
+TEST_F(TestPrettyPrint, PrimitiveTypeCustomArrayElementDelimiter) {
+  PrettyPrintOptions options{};
+  // Display array contents on one line.
+  options.skip_new_lines = true;
+  // Display maximum of 3 elements at the beginning and at the end of the array
+  options.window = 3;
+  // Use a custom array element delimiter of " | ",
+  // rather than the default delimiter (i.e. ",").
+  options.array_element_delimiter = " | ";
+
+  // Short array without ellipsis
+  {
+      std::vector<bool> is_valid = {true, true, false, true, false};
+      std::vector<int32_t> values = {1, 2, 3, 4, 5};
+      const char* expected = "[1 | 2 | null | 4 | null]";
+      CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
+  }
+
+  // Longer array with ellipsis
+  {
+      std::vector<bool> is_valid = {
+          true,
+          false,
+          true,
+          true,
+          false,
+          true,
+          false,
+          true,
+          true
+      };
+      std::vector<int32_t> values = {
+          1,
+          2,
+          3,
+          4,
+          5,
+          6,
+          7,
+          8,
+          9
+      };
+      const char* expected = "[1 | null | 3 | ... | null | 8 | 9]";
+      CheckPrimitive<Int32Type, int32_t>(options, is_valid, values, expected, false);
+  }
+}
+
 TEST_F(TestPrettyPrint, Int8) {
   static const char* expected = R"expected([
   0,
@@ -1020,6 +1067,37 @@ TEST_F(TestPrettyPrint, ChunkedArrayPrimitiveType) {
   CheckStream(chunked_array_2, {0}, expected_2);
 }
 
+TEST_F(TestPrettyPrint, ChunkedArrayPrimitiveTypeCustomArrayElementDelimiter) {
+  PrettyPrintOptions options{};
+  // Display array contents on one line.
+  options.skip_new_lines = true;
+  // Display maximum of 3 elements at the beginning and at the end of the array
+  options.window = 3;
+  // Use a custom array element delimiter of " | ",
+  // rather than the default delimiter (i.e. ",").
+  options.array_element_delimiter = " | ";
+
+  const auto chunk = ArrayFromJSON(int32(), "[1, 2, null, 4, null]");
+
+  // ChunkedArray with 1 chunk
+  {
+      const ChunkedArray chunked_array(chunk);
+
+      static const char* expected = R"expected([[1 | 2 | null | 4 | null]])expected";
+      CheckStream(chunked_array, options, expected);
+  }
+
+  // ChunkedArray with 2 chunks
+  {
+      const ChunkedArray chunked_array({chunk, chunk});
+
+      static const char* expected =
+          R"expected([[1 | 2 | null | 4 | null],[1 | 2 | null | 4 | null]])expected";
+
+      CheckStream(chunked_array, options, expected);
+  }
+}
+
 TEST_F(TestPrettyPrint, TablePrimitive) {
   std::shared_ptr<Field> int_field = field("column", int32());
   auto array = ArrayFromJSON(int_field->type(), "[0, 1, null, 3, null]");