Combine documents in a dfm by a grouping variable

Source: R/dfm_group.R

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)

Arguments

x

a dfm
groups

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.
fill

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.
force

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".

Value

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.

Examples

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