[GitHub] [arrow] edponce commented on a change in pull request #10869: ARROW-12714: [C++] String title case kernel

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

edponce commented on a change in pull request #10869:
URL: https://github.com/apache/arrow/pull/10869#discussion_r698416337



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File path: cpp/src/arrow/compute/kernels/scalar_string.cc
##########
@@ -527,6 +517,55 @@ struct Utf8CapitalizeTransform : public StringTransformBase {
 template <typename Type>
 using Utf8Capitalize = StringTransformExec<Type, Utf8CapitalizeTransform>;
 
+struct Utf8TitleTransform : public StringTransformCodepointBase {
+  int64_t Transform(const uint8_t* input, int64_t input_string_ncodeunits,
+                    uint8_t* output) {
+    uint8_t* output_start = output;
+    const uint8_t* end = input + input_string_ncodeunits;
+    const uint8_t* curr = NULLPTR;
+    uint32_t codepoint = 0;
+
+    do {
+      // Uppercase first alpha character of current word
+      while (input < end) {
+        curr = input;
+        if (ARROW_PREDICT_FALSE(!util::UTF8Decode(&curr, &codepoint))) {
+          return kTransformError;
+        }
+        if (IsCasedCharacterUnicode(codepoint)) {
+          output =
+              util::UTF8Encode(output, UTF8UpperTransform::TransformCodepoint(codepoint));
+          input = curr;
+          break;
+        }
+        output = std::copy(input, curr, output);
+        input = curr;
+      }
+
+      // Lowercase characters until a whitespace is found

Review comment:
       Thanks for catching this. I do have the incorrect semantics of what titlecase is. Lesson learned: Always verify multiple languages/sources for semantics of compute functions.




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