# tsCV

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##### Time series cross-validation

tsCV computes the forecast errors obtained by applying forecastfunction to subsets of the time series y using a rolling forecast origin.

Keywords
ts
##### Usage
tsCV(y, forecastfunction, h = 1, window = NULL, xreg = NULL, initial = 0, ...)
##### Arguments
y

Univariate time series

forecastfunction

Function to return an object of class forecast. Its first argument must be a univariate time series, and it must have an argument h for the forecast horizon.

h

Forecast horizon

window

Length of the rolling window, if NULL, a rolling window will not be used.

xreg

Exogeneous predictor variables passed to the forecast function if required.

initial

Initial period of the time series where no cross-validation is performed.

...

Other arguments are passed to forecastfunction.

##### Details

Let y contain the time series $$y_1,\dots,y_T$$. Then forecastfunction is applied successively to the time series $$y_1,\dots,y_t$$, for $$t=1,\dots,T-h$$, making predictions $$\hat{y}_{t+h|t}$$. The errors are given by $$e_{t+h} = y_{t+h}-\hat{y}_{t+h|t}$$. If h=1, these are returned as a vector, $$e_1,\dots,e_T$$. For h>1, they are returned as a matrix with the hth column containing errors for forecast horizon h. The first few errors may be missing as it may not be possible to apply forecastfunction to very short time series.

##### Value

Numerical time series object containing the forecast errors as a vector (if h=1) and a matrix otherwise. The time index corresponds to the last period of the training data. The columns correspond to the forecast horizons.

• tsCV
##### Examples
# NOT RUN {
#Fit an AR(2) model to each rolling origin subset
far2 <- function(x, h){forecast(Arima(x, order=c(2,0,0)), h=h)}
e <- tsCV(lynx, far2, h=1)

#Fit the same model with a rolling window of length 30
e <- tsCV(lynx, far2, h=1, window=30)

# }

Documentation reproduced from package forecast, version 8.13, License: GPL-3

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