CWB indexed corpora store the text of a corpus as numbers: Every token in the token stream of the corpus is identified by a unique corpus position. The string value of every token is identified by a unique integer id. The corpus library (CL) offers a set of functions to make the transitions between corpus positions, token ids, and the character string of tokens.
cl_cpos2str(
corpus,
p_attribute,
registry = Sys.getenv("CORPUS_REGISTRY"),
cpos
)
cl_cpos2id(corpus, p_attribute, registry = Sys.getenv("CORPUS_REGISTRY"), cpos)
cl_id2str(corpus, p_attribute, registry = Sys.getenv("CORPUS_REGISTRY"), id)
cl_regex2id(
corpus,
p_attribute,
regex,
registry = Sys.getenv("CORPUS_REGISTRY")
)
cl_str2id(corpus, p_attribute, str, registry = Sys.getenv("CORPUS_REGISTRY"))
cl_id2freq(corpus, p_attribute, id, registry = Sys.getenv("CORPUS_REGISTRY"))
cl_id2cpos(corpus, p_attribute, id, registry = Sys.getenv("CORPUS_REGISTRY"))name of a CWB corpus (upper case)
a p-attribute (positional attribute)
path to the registry directory, defaults to the value of the environment variable CORPUS_REGISTRY
corpus positions (integer vector)
id of a token
a regular expression
a character string
# registry directory and cpos_total will be needed in examples
cpos_total <- cl_attribute_size(
corpus = "REUTERS", attribute = "word",
attribute_type = "p", registry = get_tmp_registry()
)
# decode the token stream of the corpus (the quick way)
token_stream_str <- cl_cpos2str(
corpus = "REUTERS", p_attribute = "word",
cpos = seq.int(from = 0, to = cpos_total - 1),
registry = get_tmp_registry()
)
# decode the token stream (cpos2id first, then id2str)
token_stream_ids <- cl_cpos2id(
corpus = "REUTERS", p_attribute = "word",
cpos = seq.int(from = 0, to = cpos_total - 1),
registry = get_tmp_registry()
)
token_stream_str <- cl_id2str(
corpus = "REUTERS", p_attribute = "word",
id = token_stream_ids, registry = get_tmp_registry()
)
# get corpus positions of a token
token_to_get <- "oil"
id_oil <- cl_str2id(
corpus = "REUTERS", p_attribute = "word",
str = token_to_get, registry = get_tmp_registry()
)
cpos_oil <- cl_id2cpos <- cl_id2cpos(
corpus = "REUTERS", p_attribute = "word",
id = id_oil, registry = get_tmp_registry()
)
# get frequency of token
oil_freq <- cl_id2freq(
corpus = "REUTERS", p_attribute = "word", id = id_oil, registry = get_tmp_registry()
)
length(cpos_oil) # needs to be the same as oil_freq
#> [1] 78
# use regular expressions
ids <- cl_regex2id(
corpus = "REUTERS", p_attribute = "word",
regex = "M.*", registry = get_tmp_registry()
)
m_words <- cl_id2str(
corpus = "REUTERS", p_attribute = "word",
id = ids, registry = get_tmp_registry()
)