Forecast the actual values of a transformed time series in ARIMAX model in R











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I am fitting an ARIMAx model to my time series data. The "data" includes "Rate" as the outcome and x1, x2, and x3 as covariates and I have transformed the outcome using Box-Cox transformation. My data is split into a train and a test set and I want to forecast the test set with the actual values and not the transformed values. I have done the following:



data.train <- ts(data[1:24, ] , frequency = 4, start = c(2011, 4)  
data.test <- ts(data[25:28, ], frequency = 4, start = c(2017, 4))

covariates <- c("x1", "x2", "x3")
xreg.train <- data.train[, covariates]
xreg.test <- data.test[, covariates]

outcome <- data.train[, "Rate"]
lambda <- BoxCox.lambda(outcome)
outcome.trans <- BoxCox(outcome, lambda)

fit <- auto.arima(outcome.trans, xreg = xreg.train, trace = TRUE, stepwise = FALSE, seasonal = TRUE)


Now I want to forecast the test set with the actual values and not the transformed values:



 forecast.test <- predict(fit, newxreg = xreg.test, lambda = lambda)


Now the PROBLEM is that this predict function produces a forecast of the transformed values and not the actual values. How can I get the forecast of the actual values without doing the transformation myself.










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    I am fitting an ARIMAx model to my time series data. The "data" includes "Rate" as the outcome and x1, x2, and x3 as covariates and I have transformed the outcome using Box-Cox transformation. My data is split into a train and a test set and I want to forecast the test set with the actual values and not the transformed values. I have done the following:



    data.train <- ts(data[1:24, ] , frequency = 4, start = c(2011, 4)  
    data.test <- ts(data[25:28, ], frequency = 4, start = c(2017, 4))

    covariates <- c("x1", "x2", "x3")
    xreg.train <- data.train[, covariates]
    xreg.test <- data.test[, covariates]

    outcome <- data.train[, "Rate"]
    lambda <- BoxCox.lambda(outcome)
    outcome.trans <- BoxCox(outcome, lambda)

    fit <- auto.arima(outcome.trans, xreg = xreg.train, trace = TRUE, stepwise = FALSE, seasonal = TRUE)


    Now I want to forecast the test set with the actual values and not the transformed values:



     forecast.test <- predict(fit, newxreg = xreg.test, lambda = lambda)


    Now the PROBLEM is that this predict function produces a forecast of the transformed values and not the actual values. How can I get the forecast of the actual values without doing the transformation myself.










    share|improve this question


























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      down vote

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      I am fitting an ARIMAx model to my time series data. The "data" includes "Rate" as the outcome and x1, x2, and x3 as covariates and I have transformed the outcome using Box-Cox transformation. My data is split into a train and a test set and I want to forecast the test set with the actual values and not the transformed values. I have done the following:



      data.train <- ts(data[1:24, ] , frequency = 4, start = c(2011, 4)  
      data.test <- ts(data[25:28, ], frequency = 4, start = c(2017, 4))

      covariates <- c("x1", "x2", "x3")
      xreg.train <- data.train[, covariates]
      xreg.test <- data.test[, covariates]

      outcome <- data.train[, "Rate"]
      lambda <- BoxCox.lambda(outcome)
      outcome.trans <- BoxCox(outcome, lambda)

      fit <- auto.arima(outcome.trans, xreg = xreg.train, trace = TRUE, stepwise = FALSE, seasonal = TRUE)


      Now I want to forecast the test set with the actual values and not the transformed values:



       forecast.test <- predict(fit, newxreg = xreg.test, lambda = lambda)


      Now the PROBLEM is that this predict function produces a forecast of the transformed values and not the actual values. How can I get the forecast of the actual values without doing the transformation myself.










      share|improve this question















      I am fitting an ARIMAx model to my time series data. The "data" includes "Rate" as the outcome and x1, x2, and x3 as covariates and I have transformed the outcome using Box-Cox transformation. My data is split into a train and a test set and I want to forecast the test set with the actual values and not the transformed values. I have done the following:



      data.train <- ts(data[1:24, ] , frequency = 4, start = c(2011, 4)  
      data.test <- ts(data[25:28, ], frequency = 4, start = c(2017, 4))

      covariates <- c("x1", "x2", "x3")
      xreg.train <- data.train[, covariates]
      xreg.test <- data.test[, covariates]

      outcome <- data.train[, "Rate"]
      lambda <- BoxCox.lambda(outcome)
      outcome.trans <- BoxCox(outcome, lambda)

      fit <- auto.arima(outcome.trans, xreg = xreg.train, trace = TRUE, stepwise = FALSE, seasonal = TRUE)


      Now I want to forecast the test set with the actual values and not the transformed values:



       forecast.test <- predict(fit, newxreg = xreg.test, lambda = lambda)


      Now the PROBLEM is that this predict function produces a forecast of the transformed values and not the actual values. How can I get the forecast of the actual values without doing the transformation myself.







      r time-series transformation arima






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      edited Nov 23 at 2:14









      jsb

      1,47911426




      1,47911426










      asked Nov 20 at 17:51









      sahboor

      387




      387
























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          The forecast package does all this for you. But you need to use the forecast() function, not the predict() function.



          data.train <- ts(data[1:24,] ,frequency=4, start=c(2011,4)  
          data.test <- ts(data[25:28,], frequency=4, start=c(2017,4))

          covariates <- c("x1","x2","x3")
          xreg.train <- data.train[, covariates]
          xreg.test <- data.test[, covariates]

          outcome <- data.train[,"Rate"]
          lambda <- BoxCox.lambda(outcome)

          fit<- auto.arima(outcome, xreg=xreg.train, lambda=lambda,
          trace=TRUE, stepwise=FALSE, seasonal=TRUE, lambda=lambda)

          forecast.test <- forecast(fit, xreg=xreg.test, lambda=lambda)





          share|improve this answer























          • Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
            – sahboor
            Nov 21 at 13:32








          • 1




            Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
            – Rob Hyndman
            Nov 21 at 20:00










          • thank you so much Rob, fixed
            – sahboor
            Nov 21 at 21:30











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          up vote
          2
          down vote













          The forecast package does all this for you. But you need to use the forecast() function, not the predict() function.



          data.train <- ts(data[1:24,] ,frequency=4, start=c(2011,4)  
          data.test <- ts(data[25:28,], frequency=4, start=c(2017,4))

          covariates <- c("x1","x2","x3")
          xreg.train <- data.train[, covariates]
          xreg.test <- data.test[, covariates]

          outcome <- data.train[,"Rate"]
          lambda <- BoxCox.lambda(outcome)

          fit<- auto.arima(outcome, xreg=xreg.train, lambda=lambda,
          trace=TRUE, stepwise=FALSE, seasonal=TRUE, lambda=lambda)

          forecast.test <- forecast(fit, xreg=xreg.test, lambda=lambda)





          share|improve this answer























          • Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
            – sahboor
            Nov 21 at 13:32








          • 1




            Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
            – Rob Hyndman
            Nov 21 at 20:00










          • thank you so much Rob, fixed
            – sahboor
            Nov 21 at 21:30















          up vote
          2
          down vote













          The forecast package does all this for you. But you need to use the forecast() function, not the predict() function.



          data.train <- ts(data[1:24,] ,frequency=4, start=c(2011,4)  
          data.test <- ts(data[25:28,], frequency=4, start=c(2017,4))

          covariates <- c("x1","x2","x3")
          xreg.train <- data.train[, covariates]
          xreg.test <- data.test[, covariates]

          outcome <- data.train[,"Rate"]
          lambda <- BoxCox.lambda(outcome)

          fit<- auto.arima(outcome, xreg=xreg.train, lambda=lambda,
          trace=TRUE, stepwise=FALSE, seasonal=TRUE, lambda=lambda)

          forecast.test <- forecast(fit, xreg=xreg.test, lambda=lambda)





          share|improve this answer























          • Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
            – sahboor
            Nov 21 at 13:32








          • 1




            Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
            – Rob Hyndman
            Nov 21 at 20:00










          • thank you so much Rob, fixed
            – sahboor
            Nov 21 at 21:30













          up vote
          2
          down vote










          up vote
          2
          down vote









          The forecast package does all this for you. But you need to use the forecast() function, not the predict() function.



          data.train <- ts(data[1:24,] ,frequency=4, start=c(2011,4)  
          data.test <- ts(data[25:28,], frequency=4, start=c(2017,4))

          covariates <- c("x1","x2","x3")
          xreg.train <- data.train[, covariates]
          xreg.test <- data.test[, covariates]

          outcome <- data.train[,"Rate"]
          lambda <- BoxCox.lambda(outcome)

          fit<- auto.arima(outcome, xreg=xreg.train, lambda=lambda,
          trace=TRUE, stepwise=FALSE, seasonal=TRUE, lambda=lambda)

          forecast.test <- forecast(fit, xreg=xreg.test, lambda=lambda)





          share|improve this answer














          The forecast package does all this for you. But you need to use the forecast() function, not the predict() function.



          data.train <- ts(data[1:24,] ,frequency=4, start=c(2011,4)  
          data.test <- ts(data[25:28,], frequency=4, start=c(2017,4))

          covariates <- c("x1","x2","x3")
          xreg.train <- data.train[, covariates]
          xreg.test <- data.test[, covariates]

          outcome <- data.train[,"Rate"]
          lambda <- BoxCox.lambda(outcome)

          fit<- auto.arima(outcome, xreg=xreg.train, lambda=lambda,
          trace=TRUE, stepwise=FALSE, seasonal=TRUE, lambda=lambda)

          forecast.test <- forecast(fit, xreg=xreg.test, lambda=lambda)






          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 21 at 19:59

























          answered Nov 21 at 11:07









          Rob Hyndman

          20.2k64666




          20.2k64666












          • Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
            – sahboor
            Nov 21 at 13:32








          • 1




            Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
            – Rob Hyndman
            Nov 21 at 20:00










          • thank you so much Rob, fixed
            – sahboor
            Nov 21 at 21:30


















          • Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
            – sahboor
            Nov 21 at 13:32








          • 1




            Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
            – Rob Hyndman
            Nov 21 at 20:00










          • thank you so much Rob, fixed
            – sahboor
            Nov 21 at 21:30
















          Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
          – sahboor
          Nov 21 at 13:32






          Rob when i use your command i get this error: Error in forecast(fit, newxreg = xreg.test, : unused arguments (newxreg = xreg.test, lambda = lambda) seems like it doesnt recognize the newxreg command within the forecast function
          – sahboor
          Nov 21 at 13:32






          1




          1




          Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
          – Rob Hyndman
          Nov 21 at 20:00




          Sorry. Now fixed. you need to use xreg, not newxreg, with forecast()
          – Rob Hyndman
          Nov 21 at 20:00












          thank you so much Rob, fixed
          – sahboor
          Nov 21 at 21:30




          thank you so much Rob, fixed
          – sahboor
          Nov 21 at 21:30


















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