tCorpus$code_dictionary {corpustools}

Dictionary lookup

Description

Add a column to the token data that contains a code (the query label) for tokens that match the dictionary

Usage:

## R6 method for class tCorpus. Use as tc$method (where tc is a tCorpus object).

code_dictionary(...)

Arguments

dict

A dictionary. Can be either a data.frame or a quanteda dictionary. If a data.frame is given, it has to have a column named "string" (or use string_col argument) that contains the dictionary terms. All other columns are added to the tCorpus $tokens data. Each row has a single string, that can be a single word or a sequence of words seperated by a whitespace (e.g., "not bad"), and can have the common ? and * wildcards. If a quanteda dictionary is given, it is automatically converted to this type of data.frame with the melt_quanteda_dict function. This can be done manually for more control over labels.

token_col

The feature in tc that contains the token text.

string_col

If dict is a data.frame, the name of the column in dict that contains the dictionary lookup string

sep

A regular expression for separating multi-word lookup strings (default is " ", which is what quanteda dictionaries use). For example, if the dictionary contains "Barack Obama", sep should be " " so that it matches the consequtive tokens "Barack" and "Obama". In some dictionaries, however, it might say "Barack+Obama", so in that case sep = '\\+' should be used.

case_sensitive

logical, should lookup be case sensitive?

column

The name of the column added to $tokens. [column]_id contains the unique id of the match. If a quanteda dictionary is given, the label for the match is in the column named [column]. If a dictionary has multiple levels, these are added as [column]_l[level].

use_wildcards

Use the wildcards * (any number including none of any character) and ? (one or none of any character). If FALSE, exact string matching is used. (":-)" versus ":" "-" ")"). This is only behind the scenes for the dictionary lookup, and will not affect tokenization in the corpus.

ascii

If true, convert text to ascii before matching

verbose

If true, report progress

Value

the tCorpus

Examples

dict = data.frame(string = c('good','bad','ugl*','nice','not pret*', ':)', ':('), 
                  sentiment=c(1,-1,-1,1,-1,1,-1))
tc = create_tcorpus(c('The good, the bad and the ugly, is nice :) but not pretty :('))
tc$code_dictionary(dict)
tc$tokens