added merging_separator argument to allow for specifying chunk merge (#…

…18027)

llama-index-core/llama_index/core/node_parser/text/semantic_double_merging_splitter.py

@@ -74,6 +74,7 @@ class SemanticDoubleMergingSplitterNodeParser(NodeParser):
         merging_threshold (float): sets threshold for merging whole chunks
         max_chunk_size (int): maximum size of chunk (in characters)
         merging_range (int): How many chunks 'ahead' beyond the nearest neighbor to be merged if similar (1 or 2 available)
+        merging_separator (str): The separator to use when merging chunks. Defaults to a single space.
         sentence_splitter (Optional[Callable]): splits text into sentences
     """
 
@@ -123,6 +124,11 @@ class SemanticDoubleMergingSplitterNodeParser(NodeParser):
         ),
     )
 
+    merging_separator: str = Field(
+        default=" ",
+        description="The separator to use when merging chunks. Defaults to a single space.",
+    )
+
     sentence_splitter: Callable[[str], List[str]] = Field(
         default_factory=split_by_sentence_tokenizer,
         description="The text splitter to use when splitting documents.",
@@ -142,6 +148,7 @@ def from_defaults(
         merging_threshold: Optional[float] = 0.8,
         max_chunk_size: Optional[int] = 1000,
         merging_range: Optional[int] = 1,
+        merging_separator: Optional[str] = " ",
         sentence_splitter: Optional[Callable[[str], List[str]]] = None,
         original_text_metadata_key: str = DEFAULT_OG_TEXT_METADATA_KEY,
         include_metadata: bool = True,
@@ -162,6 +169,7 @@ def from_defaults(
             merging_threshold=merging_threshold,
             max_chunk_size=max_chunk_size,
             merging_range=merging_range,
+            merging_separator=merging_separator,
             sentence_splitter=sentence_splitter,
             original_text_metadata_key=original_text_metadata_key,
             include_metadata=include_metadata,
@@ -239,14 +247,14 @@ def _create_initial_chunks(self, sentences: List[str]) -> List[str]:
                 chunk_sentences = [chunk]
                 if len(chunk) + len(sentence) + 1 <= self.max_chunk_size:
                     chunk_sentences.append(sentence)
-                    chunk = " ".join(chunk_sentences)
+                    chunk = self.merging_separator.join(chunk_sentences)
                     new = False
                 else:
                     new = True
                     initial_chunks.append(chunk)
                     chunk = sentence
                     continue
-                last_sentences = " ".join(chunk_sentences[-2:])
+                last_sentences = self.merging_separator.join(chunk_sentences[-2:])
                 # new = False
 
             elif (
@@ -261,8 +269,8 @@ def _create_initial_chunks(self, sentences: List[str]) -> List[str]:
             ):
                 # elif nlp(last_sentences).similarity(nlp(sentence)) > self.threshold:
                 chunk_sentences.append(sentence)
-                last_sentences = " ".join(chunk_sentences[-2:])
-                chunk += " " + sentence
+                last_sentences = self.merging_separator.join(chunk_sentences[-2:])
+                chunk += self.merging_separator + sentence
             else:
                 initial_chunks.append(chunk)
                 chunk = sentence  # ""
@@ -302,7 +310,7 @@ def _merge_initial_chunks(self, initial_chunks: List[str]) -> List[str]:
                 > self.merging_threshold
                 and len(current) + len(initial_chunks[i]) + 1 <= self.max_chunk_size
             ):
-                current += " " + initial_chunks[i]
+                current += self.merging_separator + initial_chunks[i]
 
             # check if 1st and 3rd chunk are similar, if yes then merge 1st, 2nd, 3rd together
             elif (
@@ -319,7 +327,12 @@ def _merge_initial_chunks(self, initial_chunks: List[str]) -> List[str]:
                 + 2
                 <= self.max_chunk_size
             ):
-                current += " " + initial_chunks[i] + " " + initial_chunks[i + 1]
+                current += (
+                    self.merging_separator
+                    + initial_chunks[i]
+                    + self.merging_separator
+                    + initial_chunks[i + 1]
+                )
                 skip = 1
 
             # check if 1st and 4th chunk are smilar, if yes then merge 1st, 2nd, 3rd and 4th together
@@ -340,11 +353,11 @@ def _merge_initial_chunks(self, initial_chunks: List[str]) -> List[str]:
                 <= self.max_chunk_size
             ):
                 current += (
-                    " "
+                    self.merging_separator
                     + initial_chunks[i]
-                    + " "
+                    + self.merging_separator
                     + initial_chunks[i + 1]
-                    + " "
+                    + self.merging_separator
                     + initial_chunks[i + 2]
                 )
                 skip = 2