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How-To Beginner 2 min read 302 words

How to Clean and Normalize Text Data

Remove invisible characters, normalize whitespace, fix encoding issues, and standardize text for data processing.

Text Data Cleaning

Raw text data from web scraping, user input, OCR, and file imports contains invisible problems: zero-width characters, mixed line endings, non-breaking spaces, and encoding errors. Cleaning text before processing prevents downstream failures.

Invisible Character Removal

Text from web pages often contains zero-width spaces (U+200B), zero-width joiners (U+200D), soft hyphens (U+00AD), and byte order marks (U+FEFF). These characters are invisible in most editors but cause string comparisons to fail, word counts to be wrong, and data deduplication to miss matches. Strip them as the first cleaning step.

Whitespace Normalization

Multiple consecutive spaces, tabs mixed with spaces, non-breaking spaces (U+00A0), em spaces (U+2003), and thin spaces (U+2009) all appear as whitespace but are different characters. Normalize by replacing all Unicode whitespace characters with standard spaces, then collapsing multiple spaces into one. Trim leading and trailing whitespace from each line.

Line Ending Standardization

Windows uses CRLF (\r\n), Unix uses LF (\n), and classic Mac uses CR (\r). Mixed line endings in a single file cause parsing failures. Standardize to LF for web and Unix processing, CRLF for Windows-specific output. Many text processing issues traced to "mysterious extra blank lines" are actually caused by CRLF files processed by LF-expecting tools.

Unicode Normalization

The same visual character can have multiple Unicode representations. The letter "é" can be a single code point (U+00E9, NFC form) or two code points (e + combining acute accent, NFD form). Without normalization, string comparison, sorting, and searching produce inconsistent results. Use NFC normalization for general text processing and NFKC for search indexing.

Practical Cleaning Pipeline

Apply these steps in order: decode to UTF-8, apply NFKC normalization, strip zero-width and control characters, normalize whitespace, standardize line endings, trim lines. This pipeline handles the vast majority of real-world text cleaning needs without losing meaningful content.

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