This function prepares the data for k-fold cross-validation by dividing the
dataset into k folds. It creates subsets of training and testing data for
each fold without performing any analysis or fitting models.
     
    
    Usage
    crossv_k(data, y, k = 5, id = ".id")
 
     
    
    Arguments
- data
 
A data frame containing the training data.
 
- y
 
A response vector.
 
- k
 
An integer specifying the number of folds for cross-validation.
 
- id
 
A character string specifying the identifier for the output data frame.
 
 
    
    Value
    A tibble containing the training and testing data, response vectors, and fold IDs for each fold.
     
    
    Examples
    data <- iris[,-5]
y <- iris$Species
result <- crossv_k(data, y, k = 5)