feat: Add CJK-friendly substring fallback alignment and unaligned extractions visualization

[jidechao]

Summary

This PR adds a substring-based fallback alignment mechanism for CJK text (Chinese, Japanese, Korean) and a visualization panel for unaligned extractions.

Problem

When extracting from CJK text, the tokenizer often groups multiple characters into a single token. This causes token-based exact and fuzzy alignment to fail, leaving extractions without valid values and making them invisible in the visualization output.

Changes

langextract/core/data.py

• Add MATCH_SUBSTRING enum value to AlignmentStatus for fallback substring matching

langextract/resolver.py

• Implement substring fallback alignment in WordAligner after token-based alignment
• Non-overlapping span detection to prevent duplicate highlights
• Tracks occupied spans to avoid collisions with already-aligned extractions

langextract/visualization.py

• Add _build_unaligned_extractions_html() to display extractions lacking valid char_interval
• New CSS styles for the unaligned extractions panel
• Integrates unaligned panel into the attributes sidebar

Testing

Tested with Chinese text extraction where tokenizer groups characters into single tokens. Substring fallback successfully aligns previously-unaligned extractions and the visualization correctly shows any remaining unaligned items.

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[harshagm665-netizen]

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Analysis of the Issue

The root cause of the issue lies in the fact that the tokenizer often groups multiple characters into a single token when dealing with CJK text, causing token-based exact and fuzzy alignment to fail. This results in extractions lacking valid values and making them invisible in the visualization output.

Solution

To address this issue, we need to implement a substring-based fallback alignment mechanism for CJK text and add a visualization panel for unaligned extractions. The following code block provides the necessary changes:

# langextract/core/data.py
from enum import Enum

class AlignmentStatus(Enum):
    EXACT = 1
    FUZZY = 2
    SUBSTRING = 3  # Add MATCH_SUBSTRING enum value

# langextract/resolver.py
class WordAligner:
    def __init__(self, text, tokens):
        self.text = text
        self.tokens = tokens
        self.occupied_spans = []

    def align(self, extraction):
        # Token-based alignment
        for token in self.tokens:
            if token == extraction:
                return token

        # Substring fallback alignment
        for i in range(len(self.text)):
            for j in range(i + 1, len(self.text) + 1):
                substring = self.text[i:j]
                if substring in extraction and self.is_non_overlapping(i, j):
                    self.occupied_spans.append((i, j))
                    return substring

        return None

    def is_non_overlapping(self, start, end):
        for span in self.occupied_spans:
            if start < span[1] and end > span[0]:
                return False
        return True

# langextract/visualization.py
class Visualization:
    def __init__(self, extractions):
        self.extractions = extractions

    def _build_unaligned_extractions_html(self):
        html = ""
        for extraction in self.extractions:
            if not extraction.char_interval:
                html += f"<div>{extraction.text}</div>"
        return html

    def build_html(self):
        html = ""
        html += self._build_unaligned_extractions_html()
        # Integrates unaligned panel into the attributes sidebar
        return html

CSS Styles for Unaligned Extractions Panel

.unaligned-extractions-panel {
    border: 1px solid #ccc;
    padding: 10px;
}

.unaligned-extractions-panel div {
    margin-bottom: 10px;
}

I offer this code to the maintainers to use and modify as needed to fix the issue. The changes include adding a MATCH_SUBSTRING enum value to AlignmentStatus, implementing substring fallback alignment in WordAligner, and adding a visualization panel for unaligned extractions in Visualization. The CSS styles for the unaligned extractions panel are also provided.