Create indices for train and test splits.

The function creates the split indices for train and test samples (i.e. partitioning into time slices) for time series cross-validation. The user can choose between stretch and slide. The first is an expanding window approach, while the latter is a fixed window approach. The user can define the window sizes for training and testing via n_init and n_ahead, as well as the step size for increments via n_step.

Usage

split_index(
  n_total,
  n_init,
  n_ahead,
  n_skip = 0,
  n_lag = 0,
  mode = "slide",
  exceed = FALSE
)

Arguments

n_total

The total number of observations of the time series.

n_init

The number of periods for the initial training window (must be positive).

n_ahead

The forecast horizon (n-steps-ahead, must be positive).

n_skip

The number of periods to skip between windows (must be zero or positive integer).

n_lag

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

mode

Character value. Define the setup of the training window for time series cross validation. stretch is equivalent to an expanding window approach and slide is a fixed window approach.

exceed

Logical value. If TRUE, out-of-sample splits exceeding the sample size are created.

Value

A list containing the indices for train and test as integer vectors.