An n-gram is an ordered sequence of n "words" taken from a body of "text". The terms "words" and "text" can easily be interpreted literally, or with a more loose interpretation.
str_ptrA pointer to a copy of the original input string.
strlenThe length of the string.
nThe eponymous 'n' as in 'n-gram'.
ngl_ptrA pointer to the processed list of n-grams.
ngsizeThe length of the ngram list, or in other words, the number of unique n-grams in the input string.
sl_ptrA pointer to the list of words from the input string.
For example, consider the sequence "A B A C A B B". If we examine the 2-grams (or bigrams) of this sequence, they are
A B, B A, A C, C A, A B, B B
or without repetition:
A B, B A, A C, C A, B B
That is, we take the input string and group the "words" 2 at a time (because
n=2). Notice that the number of n-grams and the number of words are
not obviously related; counting repetition, the number of n-grams is equal
to
nwords - n + 1
Bounds ignoring repetition are highly dependent on the input. A correct but useless bound is
\#ngrams = nwords - (\#repeats - 1) - (n - 1)
An ngram object is an S4 class container that stores some basic
summary information (e.g., n), and several external pointers. For
information on how to construct an ngram object, see
ngram.