A bigram or digram is a sequence of two adjacent elements from a
string
String or strings may refer to:
*String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects
Arts, entertainment, and media Films
* ''Strings'' (1991 film), a Canadian anim ...
of
tokens, which are typically letters, syllables, or words. A bigram is an
''n''-gram for ''n''=2.
The frequency distribution of every bigram in a string is commonly used for simple statistical analysis of text in many applications, including in
computational linguistics
Computational linguistics is an interdisciplinary field concerned with the computational modelling of natural language, as well as the study of appropriate computational approaches to linguistic questions. In general, computational linguistics ...
,
cryptography
Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...
, and
speech recognition
Speech recognition is an interdisciplinary subfield of computer science and computational linguistics that develops methodologies and technologies that enable the recognition and translation of spoken language into text by computers. It is also ...
.
''Gappy bigrams'' or ''skipping bigrams'' are word pairs which allow gaps (perhaps avoiding connecting words, or allowing some simulation of dependencies, as in a
dependency grammar
Dependency grammar (DG) is a class of modern Grammar, grammatical theories that are all based on the dependency relation (as opposed to the ''constituency relation'' of Phrase structure grammar, phrase structure) and that can be traced back prima ...
).
Applications
Bigrams, along with other n-grams, are used in most successful
language model
A language model is a model of the human brain's ability to produce natural language. Language models are useful for a variety of tasks, including speech recognition, machine translation,Andreas, Jacob, Andreas Vlachos, and Stephen Clark (2013)"S ...
s for
speech recognition
Speech recognition is an interdisciplinary subfield of computer science and computational linguistics that develops methodologies and technologies that enable the recognition and translation of spoken language into text by computers. It is also ...
.
Bigram frequency attacks can be used in
cryptography
Cryptography, or cryptology (from "hidden, secret"; and ''graphein'', "to write", or ''-logy, -logia'', "study", respectively), is the practice and study of techniques for secure communication in the presence of Adversary (cryptography), ...
to solve
cryptograms
A cryptogram is a type of puzzle that consists of a short piece of encryption, encrypted text. Generally the cipher used to encrypt the text is simple enough that the cryptogram can be solved by hand. Substitution ciphers where each letter is ...
. See
frequency analysis.
Bigram frequency is one approach to
statistical language identification.
Some activities in
logology or recreational linguistics involve bigrams. These include attempts to find English words beginning with every possible bigram, or words containing a string of repeated bigrams, such as ''logogogue''.
Bigram frequency in the English language
The frequency of the most common letter bigrams in a large English corpus is:
th 3.56% of 1.17% io 0.83%
he 3.07% ed 1.17% le 0.83%
in 2.43% is 1.13% ve 0.83%
er 2.05% it 1.12% co 0.79%
an 1.99% al 1.09% me 0.79%
re 1.85% ar 1.07% de 0.76%
on 1.76% st 1.05% hi 0.76%
at 1.49% to 1.05% ri 0.73%
en 1.45% nt 1.04% ro 0.73%
nd 1.35% ng 0.95% ic 0.70%
ti 1.34% se 0.93% ne 0.69%
es 1.34% ha 0.93% ea 0.69%
or 1.28% as 0.87% ra 0.69%
te 1.20% ou 0.87% ce 0.65%
See also
*
Dice-Sørensen coefficient
The Dice-Sørensen coefficient (see below for other names) is a statistic used to gauge the similarity of two samples. It was independently developed by the botanists Lee Raymond Dice and Thorvald Sørensen, who published in 1945 and 1948 respec ...
*
Digraph (orthography)
A digraph () or digram is a pair of character (symbol), characters used in the orthography of a language to write either a single phoneme (distinct sound), or a sequence of phonemes that does not correspond to the normal values of the two char ...
*
Letter frequency
Letter frequency is the number of times letters of the alphabet appear on average in written language. Letter frequency analysis dates back to the Arab mathematician Al-Kindi (c. AD 801–873), who formally developed the method to break ciph ...
References
{{Natural Language Processing
Formal languages
Classical cryptography
Natural language processing