Base method extensions for corpus objects

Source: R/corpus-methods.R, R/summary.R

Extensions of base R functions for corpus objects.

# S3 method for corpus
+(c1, c2)

# S3 method for corpus
c(..., recursive = FALSE)

# S3 method for corpus
[(x, i, drop_docid = TRUE)

# S3 method for summary.corpus
print(x, ...)

Arguments

c1

corpus one to be added

c2

corpus two to be added

recursive

logical used by c() method, always set to FALSE

x

a corpus object

i

document names or indices for documents to extract.

drop_docid

if TRUE, drop docid for documents removed as the result of extraction.

Value

The + and c() operators return a corpus() object.

Indexing a corpus works in three ways, as of v2.x.x:

  • [ returns a subsetted corpus

  • [[ returns the textual contents of a subsetted corpus (similar to as.character())

  • $ returns a vector containing the single named docvars

Details

The + operator for a corpus object will combine two corpus objects, resolving any non-matching docvars() by making them into NA values for the corpus lacking that field. Corpus-level meta data is concatenated, except for source and notes, which are stamped with information pertaining to the creation of the new joined corpus.

The c() operator is also defined for corpus class objects, and provides an easy way to combine multiple corpus objects.

There are some issues that need to be addressed in future revisions of quanteda concerning the use of factors to store document variables and meta-data. Currently most or all of these are not recorded as factors, because we use stringsAsFactors=FALSE in the data.frame() calls that are used to create and store the document-level information, because the texts should always be stored as character vectors and never as factors.

See also

summary.corpus()

Examples

# concatenate corpus objects
corp1 <- corpus(data_char_ukimmig2010[1:2])
corp2 <- corpus(data_char_ukimmig2010[3:4])
corp3 <- corpus(data_char_ukimmig2010[5:6])
summary(c(corp1, corp2, corp3))
#> Corpus consisting of 6 documents, showing 6 documents:
#> 
#>          Text Types Tokens Sentences
#>           BNP  1125   3280        88
#>     Coalition   142    260         4
#>  Conservative   251    499        15
#>        Greens   322    679        21
#>        Labour   298    683        29
#>        LibDem   251    483        14
#> 

# two ways to index corpus elements
data_corpus_inaugural["1793-Washington"]
#> Corpus consisting of 1 document and 4 docvars.
#> 1793-Washington :
#> "Fellow citizens, I am again called upon by the voice of my c..."
#> 
data_corpus_inaugural[2]
#> Corpus consisting of 1 document and 4 docvars.
#> 1793-Washington :
#> "Fellow citizens, I am again called upon by the voice of my c..."
#> 

# return the text itself
data_corpus_inaugural[["1793-Washington"]]
#> [1] "Fellow citizens, I am again called upon by the voice of my country to execute the functions of its Chief Magistrate. When the occasion proper for it shall arrive, I shall endeavor to express the high sense I entertain of this distinguished honor, and of the confidence which has been reposed in me by the people of united America.\n\nPrevious to the execution of any official act of the President the Constitution requires an oath of office. This oath I am now about to take, and in your presence: That if it shall be found during my administration of the Government I have in any instance violated willingly or knowingly the injunctions thereof, I may (besides incurring constitutional punishment) be subject to the upbraidings of all who are now witnesses of the present solemn ceremony.\n\n "