Take a random sample of documents of the specified size from a corpus, with or without replacement, optionally by grouping variables or with probability weights.

corpus_sample(x, size = ndoc(x), replace = FALSE, prob = NULL, by = NULL)

Arguments

x

a corpus object whose documents will be sampled

size

a positive number, the number of documents to select; when used with by, the number to select from each group or a vector equal in length to the number of groups defining the samples to be chosen in each category of by. By defining a size larger than the number of documents, it is possible to oversample when replace = TRUE.

replace

if TRUE, sample with replacement

prob

a vector of probability weights for obtaining the elements of the vector being sampled. May not be applied when by is used.

by

optional grouping variable for sampling. This will be evaluated in the docvars data.frame, so that docvars may be referred to by name without quoting. This also changes previous behaviours for by. See news(Version >= "2.9", package = "quanteda") for details.

Value

a corpus object (re)sampled on the documents, containing the document variables for the documents sampled.

Examples

set.seed(123) # sampling from a corpus summary(corpus_sample(data_corpus_inaugural, size = 5))
#> Corpus consisting of 5 documents, showing 5 documents: #> #> Text Types Tokens Sentences Year President FirstName Party #> 1909-Taft 1437 5821 158 1909 Taft William Howard Republican #> 1845-Polk 1334 5186 153 1845 Polk James Knox Whig #> 1989-Bush 795 2673 141 1989 Bush George Republican #> 1841-Harrison 1898 9123 210 1841 Harrison William Henry Whig #> 1797-Adams 826 2577 37 1797 Adams John Federalist #>
summary(corpus_sample(data_corpus_inaugural, size = 10, replace = TRUE))
#> Corpus consisting of 10 documents, showing 10 documents: #> #> Text Types Tokens Sentences Year President FirstName #> 1953-Eisenhower.1 900 2743 119 1953 Eisenhower Dwight D. #> 1985-Reagan.1 925 2909 123 1985 Reagan Ronald #> 2001-Bush.1 621 1806 97 2001 Bush George W. #> 1957-Eisenhower.1 621 1907 92 1957 Eisenhower Dwight D. #> 1933-Roosevelt.1 743 2057 85 1933 Roosevelt Franklin D. #> 1993-Clinton.1 642 1833 81 1993 Clinton Bill #> 1841-Harrison.1 1898 9123 210 1841 Harrison William Henry #> 2001-Bush.2 621 1806 97 2001 Bush George W. #> 1885-Cleveland.1 676 1816 44 1885 Cleveland Grover #> 1889-Harrison.1 1352 4721 157 1889 Harrison Benjamin #> Party #> Republican #> Republican #> Republican #> Republican #> Democratic #> Democratic #> Whig #> Republican #> Democratic #> Republican #>
# sampling with by corp <- data_corpus_inaugural corp$century <- paste(floor(corp$Year / 100) + 1) corp$century <- paste0(corp$century, ifelse(corp$century < 21, "th", "st")) corpus_sample(corp, size = 2, by = century) %>% summary()
#> Corpus consisting of 8 documents, showing 8 documents: #> #> Text Types Tokens Sentences Year President FirstName #> 1797-Adams 826 2577 37 1797 Adams John #> 1793-Washington 96 147 4 1793 Washington George #> 1817-Monroe 1040 3677 121 1817 Monroe James #> 1873-Grant 552 1472 43 1873 Grant Ulysses S. #> 1997-Clinton 773 2436 111 1997 Clinton Bill #> 1933-Roosevelt 743 2057 85 1933 Roosevelt Franklin D. #> 2017-Trump 582 1660 88 2017 Trump Donald J. #> 2009-Obama 938 2689 110 2009 Obama Barack #> Party century #> Federalist 18th #> none 18th #> Democratic-Republican 19th #> Republican 19th #> Democratic 20th #> Democratic 20th #> Republican 21st #> Democratic 21st #>
# needs drop = TRUE to avoid empty interactions corpus_sample(corp, size = 1, by = interaction(Party, century, drop = TRUE), replace = TRUE) %>% summary()
#> Corpus consisting of 10 documents, showing 10 documents: #> #> Text Types Tokens Sentences Year President FirstName #> 1797-Adams 826 2577 37 1797 Adams John #> 1793-Washington 96 147 4 1793 Washington George #> 1893-Cleveland 821 2125 58 1893 Cleveland Grover #> 1805-Jefferson 804 2380 45 1805 Jefferson Thomas #> 1861-Lincoln 1075 3999 135 1861 Lincoln Abraham #> 1845-Polk 1334 5186 153 1845 Polk James Knox #> 1933-Roosevelt 743 2057 85 1933 Roosevelt Franklin D. #> 1921-Harding 1169 3719 148 1921 Harding Warren G. #> 2013-Obama 814 2317 88 2013 Obama Barack #> 2001-Bush 621 1806 97 2001 Bush George W. #> Party century #> Federalist 18th #> none 18th #> Democratic 19th #> Democratic-Republican 19th #> Republican 19th #> Whig 19th #> Democratic 20th #> Republican 20th #> Democratic 21st #> Republican 21st #>
# sampling sentences by document corp <- corpus(c(one = "Sentence one. Sentence two. Third sentence.", two = "First sentence, doc2. Second sentence, doc2."), docvars = data.frame(var1 = c("a", "a"), var2 = c(1, 2))) corpus_reshape(corp, to = "sentences") %>% corpus_sample(replace = TRUE, by = docid(.))
#> Corpus consisting of 5 documents and 2 docvars. #> one.1 : #> "Third sentence." #> #> one.2 : #> "Third sentence." #> #> one.3 : #> "Sentence one." #> #> two.1 : #> "Second sentence, doc2." #> #> two.2 : #> "First sentence, doc2." #>
# oversampling corpus_sample(corp, size = 5, replace = TRUE)
#> Corpus consisting of 5 documents and 2 docvars. #> two.1 : #> "First sentence, doc2. Second sentence, doc2." #> #> two.2 : #> "First sentence, doc2. Second sentence, doc2." #> #> one.1 : #> "Sentence one. Sentence two. Third sentence." #> #> one.2 : #> "Sentence one. Sentence two. Third sentence." #> #> one.3 : #> "Sentence one. Sentence two. Third sentence." #>