[R] Help using smooth.spline with zoo object

[roger koenker]

For equally spaced observations this is quite simple and available in   
various packages
but I like Gabor Grothendieck's version  (which didn't come up  
immediately in my Rseek search:

hpfilter  <-  function(y,lambda=1600)
eye <- diag(length(y))
solve(eye+lambda*crossprod(diff(eye,d=2)),y)}

url:    www.econ.uiuc.edu/~roger                Roger Koenker
email   rkoenker at uiuc.edu                       Department of Economics
vox:    217-333-4558                            University of Illinois
fax:    217-244-6678                            Champaign, IL 61820


On Apr 4, 2009, at 2:19 PM, Rob Denniker wrote:

> Can someone please show me how to smooth time series data that I  
> have in the form of a zoo object?
>
> I have a monthly economies series and all I really need is to see a  
> less jagged line when I plot it.
>
> If I do something like
>
> s <- smooth.spline(d.zoo$Y, spar = 0.2)
> plot(predict(s,index(d.zoo)), xlab = "Year")
> # not defined for Date objects
>
> and if I do something like
>
> plot(predict(s,as.numeric(index(d.zoo))), xlab = "Year")
> # one straight line, no matter the value of spar
>
> What am I doing wrong? (The unsmoothed series plots just fine - a  
> noisy upward trend)
>
> Thanks in advance.
>
> P.S. I would really just like to keep varying the penalty parameter  
> 'lambda' of a Hodrick-Prescott filter until I get a 'smooth enough'  
> series, but an archive search suggests that if I ask for this, some  
> smarty pants will reply saying that the HP filter is just the  
> smooth.spline function applied with a particular choice of lambda  
> and equally spaced observations.
>
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