Trigrams are a special case of the
''n''-gram, where ''n'' is 3. They are often used in
natural language processing for performing
statistical analysis of texts and in
cryptography
Cryptography, or cryptology (from grc, , translit=kryptós "hidden, secret"; and ''graphein'', "to write", or ''-logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of adver ...
for control and use of
ciphers and
codes.
Frequency
Context is very important, varying analysis rankings and percentages are easily derived by drawing from different sample sizes, different authors; or different document types: poetry, science-fiction, technology documentation; and writing levels: stories for children versus adults, military orders, and recipes.
Typical
cryptanalytic
Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic s ...
frequency analysis finds that the 16 most common character-level trigrams in English are:
Because encrypted messages sent by
telegraph often omit punctuation and spaces, cryptographic frequency analysis of such messages includes trigrams that straddle word boundaries. This causes trigrams such as "edt" to occur frequently, even though it may never occur in any one word of those messages.
Examples
The sentence "the quick red fox jumps over the lazy brown dog" has the following word-level trigrams:
the quick red
quick red fox
red fox jumps
fox jumps over
jumps over the
over the lazy
the lazy brown
lazy brown dog
And the word-level trigram "the quick red" has the following character-level trigrams (where an underscore "_" marks a space):
the
he_
e_q
_qu
qui
uic
ick
ck_
k_r
_re
red
References
{{Natural Language Processing
Natural language processing
Computational linguistics
Speech recognition