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initial_split creates a single binary split of the data into a training set and testing set. initial_time_split does the same, but takes the first prop samples for training, instead of a random selection. group_initial_split creates splits of the data based on some grouping variable, so that all data in a "group" is assigned to the same split. training and testing are used to extract the resulting data.


initial_split(data, prop = 3/4, strata = NULL, breaks = 4, pool = 0.1, ...)

initial_time_split(data, prop = 3/4, lag = 0, ...)

training(x, ...)

# S3 method for default
training(x, ...)

# S3 method for rsplit
training(x, ...)

testing(x, ...)

# S3 method for default
testing(x, ...)

# S3 method for rsplit
testing(x, ...)

group_initial_split(data, group, prop = 3/4, ..., strata = NULL, pool = 0.1)



A data frame.


The proportion of data to be retained for modeling/analysis.


A variable in data (single character or name) used to conduct stratified sampling. When not NULL, each resample is created within the stratification variable. Numeric strata are binned into quartiles.


A single number giving the number of bins desired to stratify a numeric stratification variable.


A proportion of data used to determine if a particular group is too small and should be pooled into another group. We do not recommend decreasing this argument below its default of 0.1 because of the dangers of stratifying groups that are too small.


These dots are for future extensions and must be empty.


A value to include a lag between the assessment and analysis set. This is useful if lagged predictors will be used during training and testing.


An rsplit object produced by initial_split() or initial_time_split().


A variable in data (single character or name) used for grouping observations with the same value to either the analysis or assessment set within a fold.


An rsplit object that can be used with the training and testing

functions to extract the data in each split.


With a strata argument, the random sampling is conducted within the stratification variable. This can help ensure that the resamples have equivalent proportions as the original data set. For a categorical variable, sampling is conducted separately within each class. For a numeric stratification variable, strata is binned into quartiles, which are then used to stratify. Strata below 10% of the total are pooled together; see make_strata() for more details.


car_split <- initial_split(mtcars)
train_data <- training(car_split)
test_data <- testing(car_split)

data(drinks, package = "modeldata")
drinks_split <- initial_time_split(drinks)
train_data <- training(drinks_split)
test_data <- testing(drinks_split)
c(max(train_data$date), min(test_data$date)) # no lag
#> [1] "2011-03-01" "2011-04-01"

# With 12 period lag
drinks_lag_split <- initial_time_split(drinks, lag = 12)
train_data <- training(drinks_lag_split)
test_data <- testing(drinks_lag_split)
c(max(train_data$date), min(test_data$date)) # 12 period lag
#> [1] "2011-03-01" "2010-04-01"

car_split <- group_initial_split(mtcars, cyl)
train_data <- training(car_split)
test_data <- testing(car_split)