forecast package v4.0

A few days ago I released ver­sion 4.0 of the fore­cast pack­age for R. There were quite a few changes and new fea­tures, so I thought it deserved a new ver­sion num­ber. I keep a list of changes in the Changelog for the pack­age, but I doubt that many peo­ple look at it. So for the record, here are the most impor­tant changes to the fore­cast pack­age made since v3.0 was released.

Expo­nen­tial smoothing

The ets() func­tion han­dles expo­nen­tial smooth­ing in the ETS frame­work, but for teach­ing pur­poses it is some­times use­ful to dis­cuss a more tra­di­tional imple­men­ta­tion that does not involve opti­miz­ing the ini­tial val­ues. The HoltWinters() func­tion in the stats pack­age attempts to do this, although the ini­tial­iza­tion used for the Holt and Holt-​​Winters meth­ods is non-​​standard, mak­ing it unsuit­able for teaching.

Con­se­quently, I’ve now mod­i­fied the ses(), holt() and hw() func­tions to allow both tra­di­tional heuris­tic ini­tial­iza­tion and ETS-​​style opti­miza­tion of ini­tial states. These func­tions also now allow damped trend and mul­ti­plica­tive trend.

Mul­ti­ple sea­son­al­ity and BATS and TBATS models

Time series with mul­ti­ple sea­sonal pat­terns (e.g., hourly data that con­tains a daily pat­tern, weekly pat­tern and an annual pat­tern) now have their own model class msts. This is use­ful when plot­ting the data, and in using the dshw() dou­ble sea­sonal Holt-​​Winters func­tion for example.

The BATS and TBATS mod­els (fit­ted using bats() and tbats()) also han­dle mul­ti­ple sea­son­al­i­ties as well as com­plex sea­son­al­i­ties (such as non-​​integer sea­son­al­ity, non-​​nested sea­son­al­ity and large period sea­son­al­ity). The mod­els are in the exponential-​​smoothing frame­work and were pro­posed by De Liv­era, Hyn­d­man and Sny­der (JASA 2011).

BATS and TBATS mod­els allow a form of time series decom­po­si­tion, and so the fit­ted objects can now plot­ted in the same way as other decom­po­si­tion objects (e.g., stl objects).

These mod­els are quite com­pu­ta­tion­ally inten­sive, and so the func­tions will use par­al­lel pro­cess­ing when it is available.

auto.arima()

This is prob­a­bly the most pop­u­lar func­tion in the pack­age, and I am always look­ing at ways to speed it up and improve the results.

  • Default model selec­tion has been switched from AIC to AICc (the bias-​​corrected form of AIC) which may affect model selec­tion for very short time series.
  • The max­i­mum orders are now restricted to less than 13 of the length of the data.
  • Par­al­lel pro­cess­ing is used where pos­si­ble when stepwise=FALSE.

Accu­racy calculations

The accuracy func­tion now works with both time series fore­casts and cross-​​sectional forecasts.

The MASE for sea­sonal time series is now defined using sea­sonal naïve fore­casts for the in-​​sample scal­ing. The MASE for cross-​​sectional fore­casts is defined using the mean fore­casts for in-​​sample scal­ing. This is con­sis­tent with my new book.

Neural net­work AR models

A new exper­i­men­tal func­tion nnetar has been intro­duced to fit a neural net­work with lagged val­ues of the time series as inputs. It is a feed-​​forward net­work with one hid­den layer, spec­i­fied using the nota­tion NNAR(p,k) to indi­cate there are p lagged inputs and k nodes in the hid­den layer. For exam­ple, a NNAR(9,5) model is a neural net­work with the last nine obser­va­tions (y_{t-1},y_{t-2},\dots,y_{t-9}) used as inputs to fore­cast the out­put y_t, and with five neu­rons in the hid­den layer. A NNAR(p,0) model is equiv­a­lent to an ARIMA(p,0,0) model but with­out the restric­tions on the para­me­ters to ensure stationarity.

With sea­sonal data, it is use­ful to also add the last observed val­ues from the same sea­son as inputs. For exam­ple, an NNAR(3,1,2)_{12} model has inputs y_{t-1}, y_{t-2}, y_{t-3} and y_{t-12}, and two neu­rons in the hid­den layer. More gen­er­ally, an NNAR(p,P,k)_m model has inputs (y_{t-1},y_{t-2},\dots,y_{t-p},y_{t-m},y_{t-2m},y_{t-Pm}) and k neu­rons in the hid­den layer. A NNAR(p,P,0)_m model is equiv­a­lent to an ARIMA(p,0,0)(P,0,0)_m model but with­out the restric­tions on the para­me­ters to ensure stationarity.

The nnetar() func­tion fits an NNAR(p,P,k)_m model. If the val­ues of p and P are not spec­i­fied, they are auto­mat­i­cally selected. For non-​​seasonal time series, the default is the opti­mal num­ber of lags (accord­ing to the AIC) for a lin­ear AR(p) model. For sea­sonal time series, the default val­ues are P=1 and p is cho­sen from the opti­mal lin­ear model fit­ted to the sea­son­ally adjusted data. If k is not spec­i­fied, it is set to k=(p+P+1)/2 (rounded to the near­est integer).

By default, 25 net­works with ran­dom start­ing val­ues are trained and their pre­dic­tions averaged.

Like many of the func­tions in the fore­cast pack­age, the default argu­ments usu­ally give rea­son­ably good fore­casts with­out the user need­ing to know much. For example:

fit <- nnetar(lynx)
plot(forecast(fit,h=20))

Because ran­dom start­ing val­ues are used, the fore­casts will be slightly dif­fer­ent each time the func­tion is called.

It is pos­si­bly to com­pute pre­dic­tion inter­vals from NNAR mod­els via sim­u­la­tion, but I have not yet imple­mented this. The func­tion will only give point fore­casts for now.

New default col­ors for fore­cast plots

The old yel­low and orange col­ors have been replaced by shades of blue-​​grey which are a lit­tle eas­ier on the eye. The darker the color, the higher the den­sity. Here is an exam­ple with 80% and 95% pre­dic­tion intervals.

library(fpp)
fit <- Arima(euretail, order=c(0,1,3), seasonal=c(0,1,1))
plot(forecast(fit,h=12))

Future devel­op­ment

Ear­lier this year I started using the pack­age for an under­grad­u­ate fore­cast­ing class which gave it a good work-​​out, and I’m also using it as the basis of my new book with George Athana­sopou­los. As a result, a lot of new func­tion­al­ity has been added, and lots of bugs have been dis­cov­ered and fixed.

The process is con­tin­u­ing and I have lots of ideas I want to imple­ment, and no doubt more bugs will be dis­cov­ered. The devel­op­ment of the fore­cast pack­age is now main­tained on github where you can see what is in devel­op­ment and report any new prob­lems. Please let me know if you find any­thing you think is an error, or if you have a suggestion.


Related Posts:


  • fer­nando

    It would be nice to have an auto­matic cross-​​validation func­tion, given the fit­ted model and the val­i­da­tion para­me­ters (training-​​set size, max Hori­zon, etc). Any­way, great job in the new version!

  • Samik

    Hi Rob, thanks for the noti­fi­ca­tion. Indeed, the ‘What’s new’ sec­tion rarely gets read. Anways, I was won­der­ing if you have an updated ver­sion of the orig­i­nal paper which detailed the auto.arima() algo­rithm, that includes the improve­ments and changes?

  • http://www.logisticadescomplicada.com/ Lean­dro Cal­le­gari Coelho

    Rob, con­grats for the devel­op­ment. I like this pack­age a lot. By the way, when­ever a new ver­sion is avail­able, the first thing I look for is the changelog/what’s new section!

  • Shea Parkes

    Thanks for all your hard work Rob! I appre­ci­ate the sub­tler default col­ors, but you’ll need to go back and update your online book to stop men­tion­ing yellow/​orange now: http://​otexts​.com/​f​p​p​/1/4/

  • Jerome

    Thank you Rob for the func­tion dshw. When I get the point of fore­cast, how could I get the fore­cast inter­val (low 0.80 and upper 0.80)? Thank you

    • http://robjhyndman.com Rob J Hyndman

      I have not imple­mented pre­dic­tion inter­vals for dshw(). Use bats() to get PI for an equiv­a­lent model.

  • BMiner

    Hey Rob, You men­tion pre­dic­tion inter­vals with ANN via sim­u­la­tion. Do you have any sources to reference?

    • http://robjhyndman.com Rob J Hyndman

      No, but a neural net­work is essen­tially a non­lin­ear autore­gres­sion and sim­u­la­tion is the most com­mon way to get PI for other non­lin­ear autore­gres­sion models.

      • Bminer

        Do you think boot­strap­ping would be a viable method (using the boot pack­age and tsboot)? I am think­ing of boot­strap­ping the series and then using each of the n mod­els cre­ated to pre­dict a new case — and thus get­ting a pre­dic­tion distribution.

        • http://robjhyndman.com Rob J Hyndman

          No. The boot­strapped series won’t allow pre­dic­tion con­di­tional on the last few val­ues of the observed series.

  • Joseph John­son

    Dr. Hyn­d­man,

    Does the ets func­tion in fore­cast pack­age v4.0 con­strain the para­me­ters to be;
    0<α<1, 0<β<α, 0<γ<1-α ?
    Would you rec­om­mend this con­straint for all mod­els?
    Does the pack­age go even fur­ther to con­straint the cer­tain mod­els as men­tioned in Chap­ter 10 of your expo­nen­tial smooth­ing book?

    Thank you for the pack­age. It has been very help­ful to me!

    • http://robjhyndman.com Rob J Hyndman

      Try read­ing the help file. It is all explained. The con­straints you men­tion are imple­mented using bounds=“usual”. The con­straints in ch10 of our book are imple­mented using bounds=“admissible”. The default is bounds=“both” mean­ing both sets of con­straints are applied.

    • Joseph John­son

      Thank you.

  • Francesco Gian­fer­rari Pini

    Hi! How can I extract the time series for the sea­sonal component(s) on a TBATS fore­cast? I can see them in the plot!

    • http://robjhyndman.com Rob J Hyndman

      Look at plot.tbats() and you will see how they are constructed.

  • Jerome

    Bon­jour Rob! I am run­ning a bats func­tion and I get this error:

    Error in checkForRemoteErrors(val) : 6 nodes pro­duced errors; first error: argu­ment is of length zero
    I have no clue to solve it. Thank you in advance for your tips.
    Jerome

    • http://robjhyndman.com Rob J Hyndman

      Try using debug() to track where the error is occurring.

  • SimonMN

    Hi Prof Hyndman,

    Is there any way to add exoge­nous inputs to the nnetar func­tion in the same way you can add exoge­nous vari­ables to the Arima or auto.arima functions?

    • http://robjhyndman.com/ Rob J Hyndman

      No, but it isn’t hard to do it using the avN­Net func­tion from the caret pack­age. Basi­cally nnetar() is fore­cast­ing using an aver­age of 20 neural nets where the inputs are lagged val­ues of the time series. You would just need to add the xreg vari­ables as inputs as well.

      • llr

        Hi Prof Hyn­d­man,
        Can you point to an exam­ple of this tech­nique? In your text­book, you show an exam­ple of avN­Net() on a cross-​​sectional dataset, which is help­ful. To imple­ment avN­Net() on a time series dataset, would you cre­ate a dataframe that holds not only dummy vari­ables for holiday/​seasonal effects but also the lagged vari­ables? Eg some­thing like avNNet(point_forecast ~ lagged_​1 + lagged_​2 + lagged_​3 + holiday_​1) where lagged_1,..,lagged_3 are the lagged vari­ables for that daily fore­cast? (And thus not use nnetar() at all?)

        • http://robjhyndman.com/ Rob J Hyndman

          Yes

  • Chris­t­ian Miller

    I don’t have any­thing sub­stan­tive to add, but I want to give a huge thanks to you Rob. This has been a help­ful and use­ful pack­age in learn­ing about fore­cast­ing and imple­ment­ing ideas. And you con­tinue to add func­tion­al­ity faster than I can keep up: it’s a great prob­lem to have.

    Greatly appre­ci­ated (and the book too!)

  • Tuan

    Hi Rob,

    is there any roadmap for com­put­ing the pre­dic­tion inter­vals of NNETAR mod­els? For some of our data (machine and net­work activ­ity mon­i­tor­ing), the NNETAR mod­els seem to ren­der the best result.

    Thank you so much for your great work.

  • Peter

    There seems to be a bug in the bats() function.

    >fit<-bats(mydata,use.box.cox=FALSE,use.trend=TRUE,use.damped.trend=FALSE,seasonal.periods=c(24,168))

    This com­mand gives a warning:

    optim() did not converge.

    The com­mand works with­out use.damped.trend=FALSE.

    regards
    Peter

    • Peter

      I am try­ing to use bats() in place of dshw().

    • http://robjhyndman.com/ Rob J Hyndman

      What makes you think it is a bug?

      • Peter

        Because it should work with­out the damped trend. That’s my opin­ion. I may be wrong.

        • http://robjhyndman.com/ Rob J Hyndman

          It does work with the damped trend. It’s only a warn­ing, and it only says that the opti­miza­tion has not yet converged.

      • Peter

        dshw() pro­duces fore­casts with­out warn­ings for the same data.

  • Leo

    Hi,
    Con­grat­u­la­tions on cre­at­ing a won­der­ful fore­cast pack­age. I have elec­tric­ity demand data con­tain­ing two sea­son­al­i­ties. When I do tbats(elec), I get just one sea­sonal period para­me­ters. If I give both sea­sonal peri­ods as input then I get para­me­ters for both. But in the later case, I am not using full power of the tbats model. Can you please say some­thing in this regard.

    • http://robjhyndman.com/ Rob J Hyndman

      I don’t know what you mean by not using the full power of the tbats model.

      • Leo

        I mean let tbats decide using the cri­te­ria men­tioned in the article.

        • http://robjhyndman.com/ Rob J Hyndman

          tbats doesn’t decide on the sea­sonal peri­ods. It chooses the num­ber of Fourier terms to use for each of the sea­sonal periods.

          • Leo

            Then how can it find the com­plex sea­son­al­ity not vis­i­ble in the plot. I remem­ber some­thing sim­i­lar men­tioned in the article.

          • Peter

            You have an option of enter­ing com­plex sea­sonal peri­ods. TBATS is not going to find them for you. TBATS only finds the para­me­ters. There are no other func­tions in R that allows this.

  • bayes40

    Hi Rob:
    Does the fore­cast pack­age you cre­ated han­dle ratio­nal dis­trib­uted lag mod­els? I am devel­op­ing hourly trans­fer func­tions that attempt to pre­dict demand for every hour of the day using 1 12 years of daily demand data with 1 12 years of input adver­tis­ing impres­sion data. I am also con­trol­ling for sea­sonal vari­ables includ­ing weekly base level demand pat­terns. I am assum­ing ARMA errors for the error terms, and I believe that a Koyck model is all I need to cap­ture the influ­ence of past adver­tis­ing on demand (request for quotes). I want to use Auto.Arima, but not sure I am sup­posed to use it with for dis­trib­u­tive lag specifications.

    • http://robjhyndman.com/ Rob J Hyndman

      No, although it does han­dle lagged covari­ates via the xreg argu­ment in the Arima() and auto.arima() func­tion. It does not han­dle a Koyck model, or any other model with ratio­nal lag struc­ture for a covari­ate. The TSA pack­age will fit the model, but not pro­duce fore­casts. I hope to imple­ment these mod­els some time, but haven’t done so yet.

    • bayes40

      Thank you so much for the quick response. Love your text book

      • bayes40

        Last ques­tion: if you were build­ing a model of adver­tis­ings effect on demand could you build an valid model using your auto arima and fore­cast pack­age by adding lagged pre­dic­tors or is there some added value in using the TSA packages?

  • Tuan

    Hi Rob,

    we are using your pack­age ‘fore­cast’ to fore­cast mil­lions of time series on hourly basis and would like to explore the option to use the incre­men­tal update of of the tbats mod­els to speed up the pro­cess­ing (i.e. given a tbats model at the time point Tn, we would like to update the model when the data point for Tn+1 arrives). I under­stand that this fea­ture is cur­rently not avail­able, and we will have to look at the source code and mod­ify it. Before we begin, can you please advise if it’s fea­si­ble? If yes, please give us some hints where to mod­ify the logic. Def­i­nitely, it’s work­ing for us, we would love to con­tribute back to the package.

    Thanks a lot for your time

    • http://robjhyndman.com/ Rob J Hyndman

      If you want to re-​​estimate the para­me­ters, then it is not really fea­si­ble as the para­me­ter opti­miza­tion is too slow. But if you want to keep the cur­rent para­me­ters, but com­pute the new fore­casts on the basis of the new data, then it should be pos­si­ble. That is on my list of pro­posed fea­tures to add to the pack­age, but it prob­a­bly won’t hap­pen in the near future. You will need to skip the para­me­ter opti­miza­tion and model selec­tion part of tbats, but still com­pute fit­ted val­ues and residuals.

      • Tuan

        Thank you so much Rob for the response.

  • Padarn

    Hi Rob. I was going to raise this on github, but it seemed to minor for an ‘issue’.

    Is there any rea­son not to have a way of spec­i­fy­ing auto­matic selec­tion of the box-​​cox trans­for­ma­tion para­me­ter (and poten­tially also a shift)?

    • http://robjhyndman.com/ Rob J Hyndman

      I’ve not come across an auto­matic method for the Box-​​Cox trans­for­ma­tion that is reli­able enough to make it the default. You can use BoxCox.lambda() which is not bad, but I get bet­ter fore­casts on aver­age with­out it.

  • mohammed jarad

    Hello
    My name is mohammed jarad,I’m stu­dent in applied sta­tis­ti­cal ,
    I have do my research about time series ‚neural net­works.
    I have prob­lem to use code of R about this code (nnetar)i don’t know haw it is
    use .
    can you help me >
    to fore­cast using this code(nnetar) .thinks you

    • http://robjhyndman.com/ Rob J Hyndman

      Read the help file.

      • mohammed jarad

        Thank you..

      • mohammed jarad

        Hi Rob, I’m do my code for my data .
        ff<- nnetar(zz, P=1, size=10, repeats=20, lambda=0.05)

        but i have prob­lem that i have not find any AIC or BIC .
        I like to tell you what i do?
        I find to (com­par­i­son between Box-​​Jenkins method­ol­ogy and Neural Net­works to pre­dict) I’m fin­ish to pre­dict by Box-​​Jenkins but I have prob­lem to find pre­dict by Neural Networks ..

        can you help my to com­par­i­son between them to my data..
        thank you so much Rob.

        • http://robjhyndman.com/ Rob J Hyndman

          Neural nets are not based on like­li­hood esti­ma­tion, so there can­not be an AIC or BIC. Use a rolling hold out sam­ple for com­par­isons instead.

          • mohammed jarad

            Thank you Rob,
            I’m going to do it.

  • Matt Weller

    I’m find­ing an error when pass­ing an lm model to the accu­racy func­tion. In R I can’t seem to access (to step through) the func­tions forecasterrors(f, x, test) and getResponse(f). Is this code avail­able and where would I be able to find it? If this debug­ging doesn’t solve it I will pre­pare a ques­tion for stack­over­flow. The error I’m get­ting kicks in at getResponse(f) as follows:

    Error in ‘[.data.frame‘(model.frame(object$model), , respon­se­var) : unde­fined columns selected

    I can see that the lm for­mula and data.table con­tain only the rel­e­vant columns cor­rectly named and I need to dig fur­ther into the func­tion which is defined in R as:

    func­tion (object, …)
    UseMethod(“getResponse”)

    Many thanks for the fore­cast pack­age, it is awe­some and I’ve only scratched the sur­face at this point.

    • http://robjhyndman.com/ Rob J Hyndman

      Can you please indi­cate what ver­sion of the pack­age you are using, and pro­vide a min­i­mal exam­ple so I can repli­cate the problem.

  • mohammed jarad

    Hi Rob, Can you please sent me any think help me on my research
    about (nnetar) I don’t find any think to help my please Rob .I’m going to find
    fore­cast­ing by (nnetar) to com­par­a­tive neural net­works with Box-​​Jenkens

    • http://robjhyndman.com/ Rob J Hyndman
      • mohammed jarad

        Thank you Rob.

      • mohammed jarad

        Hello Prof. Hyn­d­man, i do my code. I’m gen­er­at­ing an Arima model in time series. Let’s sup­pose I have n obser­va­tions. The predict.Arima func­tion from fore­cast pack­age just make pre­dic­tions for n + 1 obser­va­tion on.

        I need to make a pre­dic­tion for the n value

        (I want to pre­dict the real data)

        • http://robjhyndman.com/ Rob J Hyndman

          fit­ted() will give one-​​step fore­casts of the data used to esti­mate the model.

  • Isabella Ghe­ment

    Dear Rob,

    When one uses boot­strap­ping to derive fore­cast inter­vals, the forecast.Arima() func­tion in the fore­cast pack­age seems to report pre­dic­tion inter­vals com­puted as follows:

    qq <- qnorm(0.5 * (1 + level[i]/100))
    lower[, i] <- predpred - qq * predse
    upper[, i] <- predpred + qq * predse

    In the above, predpred  and predse rep­re­sent the mean and stan­dard devi­a­tion of the point fore­casts derived via bootstrapping.

    Is there any rea­son why the nor­mal dis­tri­b­u­tion quan­tiles are used in the deriva­tion of these fore­cast inter­vals instead of the quan­tiles cor­re­spond­ing to the boot­strap dis­tri­b­u­tion of the point forecasts?

    Also, if the boot­strap dis­tri­b­u­tion of the point fore­casts is non-​​normal (e.g., multi-​​modal), the stan­dard devi­a­tion of this dis­tri­b­u­tion may not be a sen­si­ble mea­sure of spread. Sim­i­larly, the mean of this dis­tri­b­u­tion may not be a sen­si­ble mea­sure of centre.

    Thank you very much for any clar­i­fi­ca­tions you can pro­vide.
    Isabella

    • http://robjhyndman.com/ Rob J Hyndman

      Yes, the quan­tiles would be bet­ter. I’ll add it to the list of things to do.

      • Isabella Ghe­ment

        Thanks so much, Rob! This sounds rea­son­able. It would also be help­ful to the users to have access to the boot­strap val­ues of the point fore­casts, so they can exam­ine their dis­tri­b­u­tion and assess how close to or far from nor­mal­ity this dis­tri­b­u­tion actu­ally is.

        The other thing I was won­der­ing is as follows:

        If the boot­strap dis­tri­b­u­tion of the point fore­casts looks really “wild” (e.g., sev­eral peaks, some gaps, asym­me­try, etc.), does it still make sense to report the default point fore­cast pro­duced by forecast.Arima() (which is in essence the “mean” value of the boot­strap dis­tri­b­u­tion of the point fore­casts)? Or per­haps it would be bet­ter to report instead the “median” value of the boot­strap dis­tri­b­u­tion of the point fore­casts, along with the quantile-​​based fore­cast interval?

        • http://robjhyndman.com/ Rob J Hyndman

          You can already get the boot­strap val­ues via the simulate.Arima function.

          If the dis­tri­b­u­tion of future val­ues looks wild, then you should report the whole dis­tri­b­u­tion, not just a point esti­mate or an inter­val estimate.

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