step_downsample creates a specification of a recipe step that will remove rows of a data set to make the occurrence of levels in a specific factor level equal.

step_downsample(
recipe,
...,
under_ratio = 1,
ratio = NA,
role = NA,
trained = FALSE,
column = NULL,
target = NA,
skip = TRUE,
seed = sample.int(10^5, 1),
id = rand_id("downsample")
)

# S3 method for step_downsample
tidy(x, ...)

## Arguments

recipe A recipe object. The step will be added to the sequence of operations for this recipe. One or more selector functions to choose which variable is used to sample the data. See selections() for more details. The selection should result in single factor variable. For the tidy method, these are not currently used. A numeric value for the ratio of the minority-to-majority frequencies. The default value (1) means that all other levels are sampled down to have the same frequency as the least occurring level. A value of 2 would mean that the majority levels will have (at most) (approximately) twice as many rows than the minority level. Deprecated argument; same as under_ratio Not used by this step since no new variables are created. A logical to indicate if the quantities for preprocessing have been estimated. A character string of the variable name that will be populated (eventually) by the ... selectors. An integer that will be used to subsample. This should not be set by the user and will be populated by prep. A logical. Should the step be skipped when the recipe is baked by bake.recipe()? While all operations are baked when prep.recipe() is run, some operations may not be able to be conducted on new data (e.g. processing the outcome variable(s)). Care should be taken when using skip = TRUE as it may affect the computations for subsequent operations An integer that will be used as the seed when downsampling. A character string that is unique to this step to identify it. A step_downsample object.

## Value

An updated version of recipe with the new step added to the sequence of existing steps (if any). For the tidy method, a tibble with columns terms which is the variable used to sample.

## Details

Down-sampling is intended to be performed on the training set alone. For this reason, the default is skip = TRUE. It is advisable to use prep(recipe, retain = TRUE) when preparing the recipe; in this way juice() can be used to obtain the down-sampled version of the data.

If there are missing values in the factor variable that is used to define the sampling, missing data are selected at random in the same way that the other factor levels are sampled. Missing values are not used to determine the amount of data in the minority level

For any data with factor levels occurring with the same frequency as the minority level, all data will be retained.

All columns in the data are sampled and returned by juice() and bake().

Keep in mind that the location of down-sampling in the step may have effects. For example, if centering and scaling, it is not clear whether those operations should be conducted before or after rows are removed.

## Examples

library(recipes)
library(modeldata)
data(okc)

sort(table(okc$diet, useNA = "always")) #> #> halal kosher strictly halal strictly kosher #> 11 11 18 18 #> mostly halal mostly kosher vegan strictly vegan #> 48 86 136 227 #> other mostly vegan strictly other vegetarian #> 331 335 450 665 #> strictly vegetarian mostly other mostly vegetarian strictly anything #> 874 1004 3438 5107 #> anything mostly anything <NA> #> 6174 16562 24360 ds_rec <- recipe(~., data = okc) %>% step_downsample(diet) %>% prep(training = okc, retain = TRUE) sort(table(bake(ds_rec, new_data = NULL)$diet, useNA = "always"))
#>
#>            anything               halal              kosher     mostly anything
#>                  11                  11                  11                  11
#>        mostly halal       mostly kosher        mostly other        mostly vegan
#>                  11                  11                  11                  11
#>   mostly vegetarian               other   strictly anything      strictly halal
#>                  11                  11                  11                  11
#>     strictly kosher      strictly other      strictly vegan strictly vegetarian
#>                  11                  11                  11                  11
#>               vegan          vegetarian                <NA>
#>                  11                  11                  11
# since skip defaults to TRUE, baking the step has no effect
baked_okc <- bake(ds_rec, new_data = okc)
table(baked_okc\$diet, useNA = "always")
#>
#>            anything               halal              kosher     mostly anything
#>                6174                  11                  11               16562
#>        mostly halal       mostly kosher        mostly other        mostly vegan
#>                  48                  86                1004                 335
#>   mostly vegetarian               other   strictly anything      strictly halal
#>                3438                 331                5107                  18
#>     strictly kosher      strictly other      strictly vegan strictly vegetarian
#>                  18                 450                 227                 874
#>               vegan          vegetarian                <NA>
#>                 136                 665               24360