quanteda (version 0.99.12)

as.tokens: coercion, checking, and combining functions for tokens objects

Description

Coercion functions to and from tokens objects, checks for whether an object is a tokens object, and functions to combine tokens objects.

Usage

as.tokens(x, concatenator = "_")
# S3 method for list
as.tokens(x, concatenator = "_")
# S3 method for tokens
as.list(x, ...)
# S3 method for tokens
unlist(x, recursive = FALSE, use.names = TRUE)
# S3 method for tokens
as.character(x, use.names = FALSE, ...)
is.tokens(x)
# S3 method for tokens
+(t1, t2)
# S3 method for tokens
c(...)

Arguments

x

object to be coerced or checked

concatenator

character between multi-word expressions, default is the underscore character. See Details.

...

for c.tokens only, tokens objects to be concatenated

recursive

a required argument for unlist but inapplicable to tokens objects

use.names

logical; preserve names if TRUE. For as.character and unlist only.

t1

tokens one to be added

t2

tokens two to be added

Value

as.tokens returns a quanteda tokens object.

as.list returns a simple list of characters from a tokens object.

unlist returns a simple vector of characters from a tokens object.

as.character returns a character vector from a tokens object.

is.tokens returns TRUE if the object is of class tokens, FALSE otherwise.

c(...) and + return a tokens object whose documents have been added as a single sequence of documents.

Details

The concatenator is used to automatically generate dictionary values for multi-word expressions in tokens_lookup and dfm_lookup. The underscore character is commonly used to join elements of multi-word expressions (e.g. "piece_of_cake", "New_York"), but other characters (e.g. whitespace " " or a hyphen "-") can also be used. In those cases, users have to tell the system what is the concatenator in your tokens so that the conversion knows to treat this character as the inter-word delimiter, when reading in the elements that will become the tokens.

Examples

# NOT RUN {
# create tokens object from list of characters with custom concatenator
dict <- dictionary(list(country = 'United States', 
                   sea = c('Atlantic Ocean', 'Pacific Ocean')))
lis <- list(c('The', 'United-States', 'has', 'the', 'Atlantic-Ocean', 
              'and', 'the', 'Pacific-Ocean', '.'))
toks <- as.tokens(lis, concatenator = '-')
tokens_lookup(toks, dict)

# combining tokens
toks1 <- tokens(c(doc1 = "a b c d e", doc2 = "f g h"))
toks2 <- tokens(c(doc3 = "1 2 3"))
toks1 + toks2
c(toks1, toks2)

# }