Practical guide and verification
Define what counts as the same word
Case sensitivity changes whether Word and word are duplicates. Punctuation, apostrophes, hyphens and Unicode variants can also affect token boundaries, so choose a normalization rule that matches the text you are cleaning.
Preserve order when sequence carries meaning
For prose, tags, keyword lists and transcripts, keeping the first occurrence usually preserves the original flow better than sorting. If order is not meaningful, sort only after deduplication so the transformation remains easy to audit.
Compare counts before and after
Record the original token count, unique token count and number removed. A surprisingly large reduction is a warning that the tokenizer or case rule may be collapsing items you intended to keep distinct.
Do not confuse word dedupe with line dedupe
Removing repeated words inside a text is different from removing repeated rows or lines. Use the transformation that matches the data unit, especially when working with CSV fields, addresses or multi-word labels.
Review a sample before chaining the output
If the cleaned text will feed another parser, generator or publishing step, inspect representative edge cases first. Quotes, contractions, emoji, non-Latin scripts and punctuation-heavy identifiers can behave differently from simple space-separated words.