Take a random sample of documents of the specified size from a dfm, with or without replacement, optionally by grouping variables or with probability weights.
dfm_sample(x, size = NULL, replace = FALSE, prob = NULL, by = NULL)the dfm object whose documents will be sampled
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.
if TRUE, sample with replacement
a vector of probability weights for obtaining the elements of the
vector being sampled. May not be applied when by is used.
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.
a dfm object (re)sampled on the documents, containing the document variables for the documents sampled.
set.seed(10)
dfmat <- dfm(tokens(c("a b c c d", "a a c c d d d", "a b b c")))
dfmat
#> Document-feature matrix of: 3 documents, 4 features (16.67% sparse) and 0 docvars.
#> features
#> docs a b c d
#> text1 1 1 2 1
#> text2 2 0 2 3
#> text3 1 2 1 0
dfm_sample(dfmat)
#> Document-feature matrix of: 3 documents, 4 features (16.67% sparse) and 0 docvars.
#> features
#> docs a b c d
#> text3 1 2 1 0
#> text1 1 1 2 1
#> text2 2 0 2 3
dfm_sample(dfmat, replace = TRUE)
#> Document-feature matrix of: 3 documents, 4 features (25.00% sparse) and 0 docvars.
#> features
#> docs a b c d
#> text3.1 1 2 1 0
#> text2.1 2 0 2 3
#> text3.2 1 2 1 0
# by groups
dfmat <- dfm(tokens(data_corpus_inaugural[50:58]))
dfm_sample(dfmat, by = Party, size = 2)
#> Document-feature matrix of: 4 documents, 2,999 features (74.71% sparse) and 4 docvars.
#> features
#> docs senator mathias , chief justice burger vice president bush
#> 2009-Obama 0 0 130 0 0 0 0 1 1
#> 2013-Obama 0 0 99 1 2 0 1 2 0
#> 1989-Bush 2 0 166 1 2 0 1 6 0
#> 2001-Bush 0 0 110 0 3 0 1 3 0
#> features
#> docs speaker
#> 2009-Obama 0
#> 2013-Obama 0
#> 1989-Bush 3
#> 2001-Bush 0
#> [ reached max_nfeat ... 2,989 more features ]