Apply a lumping to a nominal variable

Transforms categorical data by combining its levels according to a given lumping, such as one previously found by maximum_mutual_information_nominal(). This makes it possible to reuse a lumping, for example one learned on training data, on new data.

Usage

apply_nominal_lumping(data, lumping, level_namer = default_level_namer)

Arguments

data

Factor or character vector of the categorical data.

lumping

Named list of character vectors, where each vector contains the original levels that are combined into a new level named after the entry. If the list is unnamed, names are generated with level_namer.

level_namer

Function that takes a character vector of the original levels in a lump and returns the name of the new lumped level. Only used when lumping is unnamed. Default: concatenating the original levels with a "+" in between.

Value

A factor vector with the lumped levels.

Details

Levels that appear in the lumping but not in the data are kept as empty levels, so that applying the same lumping always yields the same factor levels. Conversely, levels that appear in the data but not in the lumping are replaced by NA, with a warning.

See also

lump_nominal() to find and apply the optimal lumping in one step.

apply_ordinal_lumping() for the ordinal analogue of this function.

Author

Daan Koning

Examples

country <- c("NL", "DE", "FR", "NL", "BE")
lumping <- list(benelux = c("NL", "BE"), other = c("DE", "FR"))
apply_nominal_lumping(country, lumping)
#> [1] benelux other   other   benelux benelux
#> Levels: benelux other