Combine documents in a dfm by a grouping variable, by summing the cell frequencies within group and creating new "documents" with the group labels.
dfm_group(x, groups = docid(x), fill = FALSE, force = FALSE)a dfm
grouping variable for sampling, equal in length to the number
of documents. 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 groups. See news(Version >= "3.0", package = "quanteda") for details.
logical; if TRUE and groups is a factor, then use all levels
of the factor when forming the new documents of the grouped object. This
will result in a new "document" with empty content for levels not observed,
but for which an empty document may be needed. If groups is a factor of
dates, for instance, then fill = TRUE ensures that the new object will
consist of one new "document" by date, regardless of whether any documents
previously existed with that date. Has no effect if the groups
variable(s) are not factors.
logical; if TRUE, group by summing existing counts, even if
the dfm has been weighted. This can result in invalid sums, such as adding
log counts (when a dfm has been weighted by "logcount" for instance using
dfm_weight()). Not needed when the term weight schemes "count" and
"prop".
dfm_group returns a dfm whose documents are equal to
the unique group combinations, and whose cell values are the sums of the
previous values summed by group. Document-level variables that have no
variation within groups are saved in docvars. Document-level
variables that are lists are dropped from grouping, even when these exhibit
no variation within groups.
corp <- corpus(c("a a b", "a b c c", "a c d d", "a c c d"),
docvars = data.frame(grp = c("grp1", "grp1", "grp2", "grp2")))
dfmat <- dfm(tokens(corp))
dfm_group(dfmat, groups = grp)
#> Document-feature matrix of: 2 documents, 4 features (25.00% sparse) and 1 docvar.
#> features
#> docs a b c d
#> grp1 3 2 2 0
#> grp2 2 0 3 3
dfm_group(dfmat, groups = c(1, 1, 2, 2))
#> Document-feature matrix of: 2 documents, 4 features (25.00% sparse) and 1 docvar.
#> features
#> docs a b c d
#> 1 3 2 2 0
#> 2 2 0 3 3
# with fill = TRUE
dfm_group(dfmat, fill = TRUE,
groups = factor(c("A", "A", "B", "C"), levels = LETTERS[1:4]))
#> Document-feature matrix of: 4 documents, 4 features (43.75% sparse) and 1 docvar.
#> features
#> docs a b c d
#> A 3 2 2 0
#> B 1 0 1 2
#> C 1 0 2 1
#> D 0 0 0 0