Extract a subset of a dfm

Returns document subsets of a dfm that meet certain conditions, including direct logical operations on docvars (document-level variables). dfm_subset functions identically to subset.data.frame(), using non-standard evaluation to evaluate conditions based on the docvars in the dfm.

dfm_subset(x, subset, drop_docid = TRUE, ...)

Arguments

x	dfm object to be subsetted
subset	logical expression indicating the documents to keep: missing values are taken as false
drop_docid	if TRUE, docid for documents are removed as the result of subsetting.
...	not used

Value

dfm object, with a subset of documents (and docvars) selected according to arguments

Details

To select or subset features, see dfm_select() instead.

When select is a dfm, then the returned dfm will be equal in document dimension and order to the dfm used for selection. This is the document-level version of using dfm_select() where pattern is a dfm: that function matches features, while dfm_subset will match documents.

See also

subset.data.frame()

Examples

corp <- corpus(c(d1 = "a b c d", d2 = "a a b e",
                 d3 = "b b c e", d4 = "e e f a b"),
               docvars = data.frame(grp = c(1, 1, 2, 3)))
dfmat <- dfm(tokens(corp))
# selecting on a docvars condition
dfm_subset(dfmat, grp > 1)
#> Document-feature matrix of: 2 documents, 6 features (41.67% sparse) and 1 docvar.
#>     features
#> docs a b c d e f
#>   d3 0 2 1 0 1 0
#>   d4 1 1 0 0 2 1
# selecting on a supplied vector
dfm_subset(dfmat, c(TRUE, FALSE, TRUE, FALSE))
#> Document-feature matrix of: 2 documents, 6 features (41.67% sparse) and 1 docvar.
#>     features
#> docs a b c d e f
#>   d1 1 1 1 1 0 0
#>   d3 0 2 1 0 1 0