Generic cross-validation for univariate and multivariate time series

crossval_ts(
  y,
  x = NULL,
  fit_func = crossvalidation::fit_lm,
  predict_func = crossvalidation::predict_lm,
  fcast_func = NULL,
  fit_params = NULL,
  p = 1,
  initial_window = 5,
  horizon = 3,
  fixed_window = TRUE,
  level = c(80, 95),
  seed = 123,
  eval_metric = NULL,
  cl = NULL,
  errorhandling = c("stop", "remove", "pass"),
  packages = c("stats", "Rcpp"),
  verbose = FALSE,
  show_progress = TRUE,
  ...
)

Arguments

y

response time series; a vector or a matrix

x

input covariates' matrix (optional) for ML models

fit_func

a function for fitting the model (if validation of ML model)

predict_func

a function for predicting values from the model (if validation of ML model)

fcast_func

time series forecasting function (e.g forecast::thetaf)

fit_params

a list; additional (model-specific) parameters to be passed to fit_func

p

a float; percentage of original data in the training/testing procedure, default is 1 and must be > 0.5.

initial_window

an integer; the initial number of consecutive values in each training set sample

horizon

an integer; the number of consecutive values in test set sample

fixed_window

a boolean; if FALSE, all training samples start at 1

level

a numeric vector; confidence levels for prediction intervals.

seed

random seed for reproducibility of results

eval_metric

a function measuring the test errors; if not provided: RMSE for regression and accuracy for classification

cl

an integer; the number of clusters for parallel execution

errorhandling

specifies how a task evalution error should be handled. If value is "stop", then execution will be stopped if an error occurs. If value is "remove", the result for that task will not be returned. If value is "pass", then the error object generated by task evaluation will be included with the rest of the results. The default value is "stop".

packages

character vector of packages that the tasks depend on

verbose

logical flag enabling verbose messages. This can be very useful for troubleshooting.

show_progress

show evolution of the algorithm

...

additional parameters

Examples



require(forecast)
#> Loading required package: forecast
data("AirPassengers")

# Example 1 -----

res <- crossval_ts(y=AirPassengers, initial_window = 10,
horizon = 3, fcast_func = forecast::thetaf)
#> 
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print(colMeans(res))
#>           ME         RMSE          MAE          MPE         MAPE 
#>  2.657082195 51.427170382 46.511874693  0.003423843  0.155428590 


# Example 2 -----

if (FALSE) {
fcast_func <- function (y, h, ...)
{
      forecast::forecast(forecast::auto.arima(y, ...),
      h=h, ...)
}

res <- crossval_ts(y=AirPassengers, initial_window = 10, horizon = 3,
fcast_func = fcast_func)
print(colMeans(res))
}


# Example 3 -----

fcast_func <- function (y, h, ...)
{
      forecast::forecast(forecast::ets(y, ...),
      h=h, ...)
}

res <- crossval_ts(y=AirPassengers,
initial_window = 10, horizon = 3, fcast_func = fcast_func)
#> 
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print(colMeans(res))
#>           ME         RMSE          MAE          MPE         MAPE 
#>  5.606310555 45.344040192 40.688899803 -0.008682302  0.136229866 


# Example 4 -----

xreg <- cbind(1, 1:length(AirPassengers))
res <- crossval_ts(y=AirPassengers, x=xreg, fit_func = crossvalidation::fit_lm,
predict_func = crossvalidation::predict_lm,
initial_window = 10,
horizon = 3,
fixed_window = TRUE)
#> 
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print(colMeans(res))
#>          ME        RMSE         MAE         MPE        MAPE 
#>  0.16473829 71.42382836 67.01472299  0.02345201  0.22106607 


# Example 5 -----

res <- crossval_ts(y=AirPassengers, fcast_func = forecast::thetaf,
initial_window = 10,
horizon = 3,
fixed_window = TRUE)
#> 
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print(colMeans(res))
#>           ME         RMSE          MAE          MPE         MAPE 
#>  2.657082195 51.427170382 46.511874693  0.003423843  0.155428590 


#' # Example 6 -----

xreg <- cbind(1, 1:length(AirPassengers))
res <- crossval_ts(y=AirPassengers, x=xreg, fit_func = crossvalidation::fit_lm,
predict_func = crossvalidation::predict_lm,
initial_window = 10,
horizon = 3,
fixed_window = TRUE)
#> 
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print(colMeans(res))
#>          ME        RMSE         MAE         MPE        MAPE 
#>  0.16473829 71.42382836 67.01472299  0.02345201  0.22106607 


# Example 7 -----

x <- ts(matrix(rnorm(50), nrow = 25))

fcast_func <- function(y, h = 5, type_forecast=c("mean", "median"))
{
 type_forecast <- match.arg(type_forecast)

 if (type_forecast == "mean")
 {
  means <- colMeans(y)
  return(list(mean = t(replicate(n = h, expr = means))))
 } else {
  medians <- apply(y, 2, median)
  return(list(mean = t(replicate(n = h, expr = medians))))
 }

}

print(fcast_func(x))
#> $mean
#>        Series 1   Series 2
#> [1,] -0.1371003 0.01822443
#> [2,] -0.1371003 0.01822443
#> [3,] -0.1371003 0.01822443
#> [4,] -0.1371003 0.01822443
#> [5,] -0.1371003 0.01822443
#> 

res <- crossval_ts(y = x, fcast_func = fcast_func, fit_params = list(type_forecast = "median"))
#> 
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colMeans(res)
#>          ME        RMSE         MAE         MPE        MAPE 
#>  0.05169141  1.06782797  0.86333229 -1.45868400  3.63199960 

res <- crossval_ts(y = x, fcast_func = fcast_func, fit_params = list(type_forecast = "mean"))
#> 
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colMeans(res)
#>          ME        RMSE         MAE         MPE        MAPE 
#>  0.05447259  1.09506956  0.84983668 -1.46797344  2.84963644 

# Example 8 -----

eval_metric <- function(predicted, observed)
{
  error <- observed - predicted

  res <- apply(error, 2, function(x) sqrt(mean(x ^ 2, na.rm = FALSE)))

  return(res)
}

res <- crossval_ts(y = x, fcast_func = fcast_func, fit_params = list(type_forecast = "mean"),
eval_metric = eval_metric)
#> 
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colMeans(res)
#>  Series 1  Series 2 
#> 0.9388166 1.1620209