corpustools (version 0.5.1)

search_contexts: Search for documents or sentences using Boolean queries

Description

Search for documents or sentences using Boolean queries

Usage

search_contexts(
  tc,
  query,
  code = NULL,
  feature = "token",
  context_level = c("document", "sentence"),
  not = F,
  verbose = F,
  as_ascii = F
)

Value

A contextHits object, which is a list with $hits (data.frame with locations) and $queries (copy of queries for provenance)

Arguments

tc

a tCorpus

query

A character string that is a query. See details for available query operators and modifiers. Can be multiple queries (as a vector), in which case it is recommended to also specifiy the code argument, to label results.

code

If given, used as a label for the results of the query. Especially usefull if multiple queries are used.

feature

The name of the feature column

context_level

Select whether the queries should occur within while "documents" or specific "sentences". Returns results at the specified level.

not

If TRUE, perform a NOT search. Return the articles/sentences for which the query is not found.

verbose

If TRUE, progress messages will be printed

as_ascii

if TRUE, perform search in ascii.

Details

Brief summary of the query language

The following operators and modifiers are supported:

• The standaard Boolean operators: AND, OR and NOT. As a shorthand, an empty space can be used as an OR statement, so that "this that those" means "this OR that OR those". NOT statements stricly mean AND NOT, so should only be used between terms. If you want to find everything except certain terms, you can use * (wildcard for anything) like this: "* NOT (this that those)".

• For complex queries parentheses can (and should) be used. e.g. '(spam AND eggs) NOT (fish and (chips OR albatros))

• Wildcards ? and *. The questionmark can be used to match 1 unknown character or no character at all, e.g. "?at" would find "cat", "hat" and "at". The asterisk can be used to match any number of unknown characters. Both the asterisk and questionmark can be used at the start, end and within a term.

• Multitoken strings, or exact strings, can be specified using quotes. e.g. "united states"

• tokens within a given token distance can be found using quotes plus tilde and a number specifiying the token distance. e.g. "climate chang*"~10

• Alternatively, angle brackets (<>) can be used instead of quotes, which also enables nesting exact strings in proximity/window search

• Queries are not case sensitive, but can be made so by adding the ~s flag. e.g. COP~s only finds "COP" in uppercase. The ~s flag can also be used on quotes to make all terms within quotes case sensitive, and this can be combined with the token proximity flag. e.g. "Marco Polo"~s10

Examples

text = c('A B C', 'D E F. G H I', 'A D', 'GGG')
tc = create_tcorpus(text, doc_id = c('a','b','c','d'), split_sentences = TRUE)
tc$tokens

hits = search_contexts(tc, c('query label# A AND B', 'second query# (A AND Q) OR ("D E") OR I'))
hits          ## print shows number of hits
hits$hits     ## hits is a list, with hits$hits being a data.frame with specific contexts
summary(hits) ## summary gives hits per query

## sentence level
hits = search_contexts(tc, c('query label# A AND B', 'second query# (A AND Q) OR ("D E") OR I'),
                          context_level = 'sentence')
hits$hits     ## hits is a list, with hits$hits being a data.frame with specific contexts

# \donttest{

## query language examples

## single term
search_contexts(tc, 'A')$hits

search_contexts(tc, 'G*')$hits    ## wildcard *
search_contexts(tc, '*G')$hits    ## wildcard *
search_contexts(tc, 'G*G')$hits   ## wildcard *

search_contexts(tc, 'G?G')$hits   ## wildcard ?
search_contexts(tc, 'G?')$hits    ## wildcard ? (no hits)

## boolean
search_contexts(tc, 'A AND B')$hits
search_contexts(tc, 'A AND D')$hits
search_contexts(tc, 'A AND (B OR D)')$hits

search_contexts(tc, 'A NOT B')$hits
search_contexts(tc, 'A NOT (B OR D)')$hits


## sequence search (adjacent words)
search_contexts(tc, '"A B"')$hits
search_contexts(tc, '"A C"')$hits ## no hit, because not adjacent

search_contexts(tc, '"A (B OR D)"')$hits ## can contain nested OR
## cannot contain nested AND or NOT!!

search_contexts(tc, '')$hits ## can also use <> instead of "".

## proximity search (using ~ flag)
search_contexts(tc, '"A C"~5')$hits ## A AND C within a 5 word window
search_contexts(tc, '"A C"~1')$hits ## no hit, because A and C more than 1 word apart

search_contexts(tc, '"A (B OR D)"~5')$hits ## can contain nested OR
search_contexts(tc, '"A "~5')$hits    ## can contain nested sequence (must use <>)
search_contexts(tc, '>~5')$hits    ## (<> is always OK, but cannot nest quotes in quotes)
## cannot contain nested AND or NOT!!


## case sensitive search
search_contexts(tc, 'g')$hits     ## normally case insensitive
search_contexts(tc, 'g~s')$hits   ## use ~s flag to make term case sensitive

search_contexts(tc, '(a OR g)~s')$hits   ## use ~s flag on everything between parentheses
search_contexts(tc, '(a OR G)~s')$hits   ## use ~s flag on everything between parentheses

search_contexts(tc, '"a b"~s')$hits   ## use ~s flag on everything between quotes
search_contexts(tc, '"A B"~s')$hits   ## use ~s flag on everything between quotes

# }