[R] Using sapply instead of for loop

Charles Determan Jr deter088 at umn.edu
Wed Nov 19 16:10:31 CET 2014 

Amit,

Even if you aren't getting an error with your original global variables it
is far better practice to avoid global variables to make you code much more
stable.  Of course you ultimately get to decide how your code is written.

That said, your error from the modified far function to include the
variables is because you added too much to the sapply statement.  Here is
what it should look like:

            A<-sapply((1:Permax),function(p) far(p, i, j, k, l, m,n,
ervalue),simplify=FALSE)

You can think apply statements as nothing more than a for loop that has
been made 'pretty'.  You wanted to iterate from 1:Permax and use the other
variables, therefore you only have the anonymous function (i.e.
function(p)) only include the iterator and supply the other values from
your nested for loops to the function.  When I run this with you code,
making sure the function accepts the extra parameters, the A array appears
to fill appropriately whereby most are 'NA' as specified by your 'far'
function.  Is this what you expect?


On Wed, Nov 19, 2014 at 8:16 AM, Amit Thombre <amitmt at techmahindra.com>
wrote:

>  Charles ,
>
> I am not getting an error . The final array A does not have the values in
> it. Here is the reproducible code.  I have even tried using paasing ervalue
> as a parameter to the function far.
>
>
> -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> errf<-function(act, res, testsize, flag)
> {
> j=1
> if(flag==1)
> {
> j<-nrow(d)-testsize
> }
>
> print(act)
> print(res)
> print(flag)
> diff<-0
> s<-0
> # loop for iterating to each value of the actual value and finding the
> difference with thepredicted value
> for (mn in 1:length(act))
> {
> cat("Value of mn in err", mn)
> cat("Value of j in err", j)
> cat("Value of res[j] in err", res[j])
> diff<-(act[mn]-res[j])
> print(act[mn])
> print(res[j])
> print(diff)
> s<-s+(diff*diff)
>
> j<-j+1
> }
>
> er1<-sqrt(s/length(act)) #forecasting error
> print(er1)
> return(er1)
> }
>
>
>
> far<-function(p)
> {
>
> cat("does it come here value of p", p)
> tryCatch({
> air.model <-Arima(tsa,order=c(i-1,j-1,k-1),
> seasonal=list(order=c(l-1,m-1,n-1),period=p-1), lambda=lbda)  # the arima
> model
>
> f<- forecast(air.model,h=testsize1) # for getting the error
>
> ervalue[i,j,k,l,m,n,p]<-errf(act1,f$mean,testsize1,flagarima)
>
> }, error=function(e)
> {
>
> return(NA)
> }
> )
> cat("Value of error", ervalue[i,j,k,l,m,n,p])
> cat("Value of i,j,k,l,m,n,p", i, j, k, l, m, n,p)
> print(ervalue)
> return(ervalue)
> }
> ---------------------------
> library('TTR')
> library('forecast')
> library('timeSeries')
> library('xts')
> library('RODBC')
>
>
> maxval=2  # set the array size as well as the maximum parameter value here.
> pmax=maxval  # set max p value of the ARIMA model
> dmax=maxval  # set max d value of the ARIMA model
> qmax=maxval  # set max q value of the ARIMA model
> Pmax=maxval  # set max P value of the ARIMA model
> Dmax=maxval  # set max D value of the ARIMA model
> Qmax=maxval  # set max Q value of the ARIMA model
> Permax=2     # maximum value of period.
> freq=12
> d<-c(10, 13, 14, 4, 5, 6, 7, 10, 12, 13, 14, 20, 3, 4, 5, 19, 23, 21, 18,
> 19, 21, 14, 15, 16, 17, 12, 20, 19, 17)
> st=2013   # start year value for getting the time series
> month=4
> tsa<-ts(d, frequency=freq, start=c(st,month))  # store the data in tsa as
> the time
>
> A<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval, 2)) # depdending
> on the max value set the , also it stores the AIC valuearray size
> er<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval,2)) # depdending
> on the max value set the , stores the error value.array size
> ervalue<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval, 2)) #
> depdending on the max value set the , stores the error value.array size
> erval1<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval, 2)) #
> depdending on the max value set the , stores the error value.array size
> for (i in 1:pmax)
> {
> for (j in 1:dmax)
> {
> for (k in 1:qmax)
> {
> for (l in 1:Pmax)
> {
> for (m in 1:Dmax)
> {
> for (n in 1:Qmax)
> {
> A<-sapply((1:Permax),function(p) far(p),simplify=FALSE)
>
> }
> }
> }
> }
> }  #for looping through period value
> }
>
>
>
>
>
>  ------------------------------
> *From:* Charles Determan Jr [deter088 at umn.edu]
> *Sent:* Wednesday, November 19, 2014 7:05 PM
> *To:* Amit Thombre
> *Cc:* r-help at r-project.org
> *Subject:* Re: [R] Using sapply instead of for loop
>
>   Amit,
>
>  Your question isn't necessarily complete.  You haven't provided a
> reproducible example of your data or an error message.  At first glance you
> aren't passing anything to your 'far' function except for 'p' and yet it
> uses i,j,k,l,m,n,testsize1, and act1.  You should generally try to avoid
> global variables as they can lead to broken code.  You should redefine your
> function with all the needed parameters and try again.
>
>  Regards,
>
> On Wed, Nov 19, 2014 at 3:47 AM, Amit Thombre <amitmt at techmahindra.com>
> wrote:
>
>> I am trying to replace a for loop by using sapply, The code is for
>> forecasting using arima. The code is as follows:-
>> -------------------------------------------------------
>> far<-function(p)
>> {
>>
>> cat("does it come here value of p", p)
>> tryCatch({
>> air.model <-Arima(tsa,order=c(i-1,j-1,k-1),
>> seasonal=list(order=c(l-1,m-1,n-1),period=p-1), lambda=lbda)  # the arima
>> model
>>
>> f<- forecast(air.model,h=testsize1) # for getting the error
>>
>> ervalue[i,j,k,l,m,n,p]<-errf(act1,f$mean,testsize1,flagarima)
>>
>> }, error=function(e)
>> {
>>
>> return(NA)
>> }
>> )
>> cat("Value of error", ervalue[i,j,k,l,m,n,p])
>> cat("Value of i,j,k,l,m,n,p", i, j, k, l, m, n,p)
>> print(ervalue)
>> return(ervalue)
>> }
>> ---------------------------
>> maxval=2  # set the array size as well as the maximum parameter value
>> here.
>> pmax=maxval  # set max p value of the ARIMA model
>> dmax=maxval  # set max d value of the ARIMA model
>> qmax=maxval  # set max q value of the ARIMA model
>> Pmax=maxval  # set max P value of the ARIMA model
>> Dmax=maxval  # set max D value of the ARIMA model
>> Qmax=maxval  # set max Q value of the ARIMA model
>> Permax=2     # maximum value of period.
>>
>> st=2013   # start year value for getting the time series
>> month=4 d<-c(10, 13, 14, 4, 5, 6, 7, 10, 12, 13, 14, 20, 3, 4, 5, 19, 23,
>> 21, 18, 19, 21, 14, 15, 16, 17, 12, 20, 19, 17)
>> tsa<-ts(d, frequency=freq, start=c(st,month))  # store the data in tsa
>> as  the time
>>
>> A<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval, 2)) # depdending
>> on the max value set the , also it stores the AIC valuearray size
>> ervalue<-array(, c(maxval,maxval,maxval,maxval,maxval,maxval, 2)) #
>> depdending on the max value set the , stores the error value.array size
>>
>> for (i in 1:pmax)
>> {
>> for (j in 1:dmax)
>> {
>> for (k in 1:qmax)
>> {
>> for (l in 1:Pmax)
>> {
>> for (m in 1:Dmax)
>> {
>> for (n in 1:Qmax)
>> {
>> A<-sapply((1:Permax),function(p) far(p),simplify=FALSE)
>>
>> }
>> }
>> }
>> }
>> }  #for looping through period value
>> }
>> ------------------------------------------------------------------
>> The sapply replaces the for loop
>> for (p in 1:Permax)
>> {
>> cat("does it come here value of p", p)
>> tryCatch({
>> air.model <-Arima(tsa,order=c(i-1,j-1,k-1),
>> seasonal=list(order=c(l-1,m-1,n-1),period=p), lambda=lbda)  # the arima
>> model
>> A[i,j,k,l,m,n,p]<-AIC(air.model)
>> f<- forecast(air.model,h=testsize1) # for getting the error
>> er[i,j,k,l,m,n,p]<-errf(act1,f$mean,testsize1,flagarima)
>> }, error=function(e)
>> {
>>
>> return(NA)
>> }
>> )
>>  cat("Value of error", er[i,j,k,l,m,n,p])
>>  cat("Value of i,j,k,l,m,n,p", i, j, k, l, m, n,p)
>> }
>> --------------------------------------------------------------------------
>> Now the er[I,j,k,l,m,n,p] I.e the error get populated but on every call
>> to the function far() the array loses the previous value and gets replaced
>> with NA and gets the newly calculated error value. Finally the array A gets
>> populated with only the latest value and does not hold the old values.
>> Please help
>>
>>
>>
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>
>
>
>  --
>  Dr. Charles Determan, PhD
> Integrated Biosciences
>
> ------------------------------
>
> ============================================================================================================================
> Disclaimer: This message and the information contained herein is
> proprietary and confidential and subject to the Tech Mahindra policy
> statement, you may review the policy at
> http://www.techmahindra.com/Disclaimer.html externally
> http://tim.techmahindra.com/tim/disclaimer.html internally within
> TechMahindra.
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-- 
Dr. Charles Determan, PhD
Integrated Biosciences

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