Character N-Grams for Robustness
Handle typos and rare words.
Character N-Grams for Robustness is a free NLP Academy lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the NLP Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Word Features Are Fragile
Word-level features break on typos and rare spellings. The model sees runnning as a brand-new word, so a single slip can lose all its signal.
Drop Down to Characters
Instead of whole words, we slice text into short chunks of letters. These overlapping pieces are called character n-grams.
What a 3-gram Looks Like
For the word cat, character 3-grams are simple letter triples. They slide across the text one position at a time to form overlapping chunks.
word = "happy"
grams = [word[i:i+3] for i in range(len(word)-2)]Why They Survive Typos
The words run and runn share most of their character grams. So a typo changes only a few features instead of erasing the whole word.
Catching Word Families
play, playing, and player all share the gram pla. Character grams quietly link related forms without any stemming step.
Great for Messy Text
Social media, usernames, and product codes are full of odd spellings. Character grams stay robust where word features fall apart.
Switching On Char Mode
scikit-learn makes this one parameter. Set analyzer to char and pick an ngram_range to extract character grams instead of words.
from sklearn.feature_extraction.text import TfidfVectorizer
vec = TfidfVectorizer(analyzer="char", ngram_range=(3, 5))char_wb Respects Words
The char_wb analyzer only makes grams inside word boundaries, padding each word. It keeps the robustness while avoiding grams that span two words.
vec = TfidfVectorizer(analyzer="char_wb", ngram_range=(2, 4))Handy for Other Languages
Languages that glue words together or have rich endings are tough for word tokenizers. Character grams sidestep that and stay language-friendly.
The Cost: Bigger Features
Character grams create many more features than words do. That extra dimensionality needs more memory, so keep the range tight.
Best as a Teammate
Character grams shine when combined with word features, not as a replacement. Together they cover both meaning and robustness. 💪
Quick Check
Why do character n-grams handle typos so well?
Recap
Character n-grams slice text into letter chunks, survive typos, and link word families. Use analyzer char in scikit-learn alongside word features. ✅
Frequently asked questions
Is the “Character N-Grams for Robustness” lesson free?
Yes — the full text of “Character N-Grams for Robustness” is free to read here on the web, and the NLP Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the NLP Academy course, upgrade to CoddyKit PRO.
What will I learn in “Character N-Grams for Robustness”?
Handle typos and rare words. You practise NLP Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start NLP Academy?
No prior experience is required. NLP Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Character N-Grams for Robustness” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this NLP Academy lesson?
Yes. Every NLP Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Beyond Bag-of-Words
- Character N-Grams for Robustness
- Combining Multiple Feature Types
- Scaling and Selecting Features