uros-db commented on code in PR #47771:
URL: https://github.com/apache/spark/pull/47771#discussion_r1718413251


##########
common/unsafe/src/main/java/org/apache/spark/sql/catalyst/util/CollationAwareUTF8String.java:
##########
@@ -1267,6 +1268,119 @@ public static UTF8String[] icuSplitSQL(final UTF8String 
string, final UTF8String
     return strings.toArray(new UTF8String[0]);
   }
 
+  /**
+   * Title casing a string according to a new behaviour.
+   * Iterates over the string and title cases the first character in each 
word, and lowercases
+   * every other character.
+   * Handles lowercasing greek sigma(Σ) separately, taking into account if
+   * it should be a small final sigma(ς) or small non-final sigma(σ).
+   * Words are separated by ASCII space(\u0020).
+   *
+   * @param target UTF8String to be title cased
+   * @return title cased target
+   */
+  public static UTF8String toTitleCaseICU(UTF8String target) {
+
+    Iterator<Integer> codepointIterator = target.
+            
codePointIterator(CodePointIteratorType.CODE_POINT_ITERATOR_MAKE_VALID);
+
+    // building the title cased target with sb
+    StringBuilder sb=new StringBuilder();
+    // newWord is true if the current character is the beginning of a word, 
false otherwise
+    // it is true on the i-th character if i==0 or target at (i-1)-th 
character is ' '
+    boolean newWord = true;
+    // we are maintaining if the current character is preceded by a cased 
letter
+    // this is used when lowercasing Σ, to figure out if it should be 
lowercased into σ or ς
+    boolean precededByCasedLetter = false;
+
+    // byte offset in target's byte array pointing to the beginning of the 
character that we
+    // need to process next(this is only actually used in 
appendLowerCasedGreekCapitalSigma)
+    int offset = 0;
+
+    while(codepointIterator.hasNext()) {
+      int codepoint = codepointIterator.next();
+      // appending the correctly cased character onto sb
+      appendTitleCasedCodepoint(sb, codepoint, newWord, precededByCasedLetter, 
target, offset);
+      // updating newWord, precededByCasedLetter and offset to be ready for
+      // the next character that we will process
+      newWord = (codepoint == ASCII_SPACE_CODEPOINT);
+      if(!UCharacter.hasBinaryProperty(codepoint, UProperty.CASE_IGNORABLE)){
+        precededByCasedLetter = UCharacter.hasBinaryProperty(codepoint, 
UProperty.CASED);
+      }
+      offset+= UTF8String.numBytesForFirstByte(target.getByte(offset));
+    }
+    return UTF8String.fromString(sb.toString());
+  }
+
+  private static void appendTitleCasedCodepoint(StringBuilder sb, int 
codepoint,
+                                                boolean isAfterAsciiSpace,
+                                                boolean precededByCasedLetter, 
UTF8String target,
+                                                int offset) {
+    if(isAfterAsciiSpace) {
+      // titlecasing a character if it is in the beginning of a new word
+      sb.append(codepointToTitleString(codepoint));
+      return;
+    }
+    if(codepoint == CAPITAL_SIGMA) {
+      // handling Σ separately

Review Comment:
   ```suggestion
         // Handling capital Greek letter sigma ('Σ') separately.
   ```



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