Uses a cost matrix to create a classification measure. True labels must be arranged in columns, predicted labels must be arranged in rows. The cost matrix is stored as slot $costs. Costs are aggregated with the mean.


R6::R6Class() inheriting from MeasureClassif.


MeasureClassifCosts$new(costs = NULL, normalize = TRUE)
  • costs :: matrix()
    Numeric matrix of costs (truth in columns, predicted response in rows).

  • normalize :: logical(1)
    If TRUE, calculate the mean costs instead of the total costs.

See also

Dictionary of Measures: mlr_measures for a complete table of all (also dynamically created) Measure implementations.


# get a cost sensitive task task = tsk("german_credit") # cost matrix as given on the UCI page of the german credit data set # costs = matrix(c(0, 5, 1, 0), nrow = 2) dimnames(costs) = list(truth = task$class_names, predicted = task$class_names) print(costs)
#> predicted #> truth good bad #> good 0 1 #> bad 5 0
# mlr3 needs truth in columns, predictions in rows costs = t(costs) # create measure which calculates the absolute costs m = msr("classif.costs", id = "german_credit_costs", costs = costs, normalize = FALSE) # fit models and calculate costs learner = lrn("classif.rpart") rr = resample(task, learner, rsmp("cv", folds = 3)) rr$aggregate(m)
#> german_credit_costs #> 300.6667