[R] NOT-SO-SIMPLE function!

[Moshe Olshansky]

Just a correction - it should be:

> x <- c(3,2,0,1,0,2,0,0,1,0,0,0,0,4,1)
> y <- rep(NA,length(x))
> z <- which(x != 0)
> l <- z - c(0,z[-length(z)])
> y[z] <- log(x[z]/l)
> y
 [1]  1.0986123  0.6931472         NA -0.6931472         NA  0.0000000         NA         NA -1.0986123
[10]         NA         NA         NA         NA -0.2231436  0.0000000



--- On Tue, 3/6/08, Moshe Olshansky <m_olshansky at yahoo.com> wrote:

> From: Moshe Olshansky <m_olshansky at yahoo.com>
> Subject: Re: [R] NOT-SO-SIMPLE function!
> To: "T.D.Rudolph" <prairie.picker at gmail.com>, marc_schwartz at comcast.net
> Cc: r-help at r-project.org
> Received: Tuesday, 3 June, 2008, 12:09 PM
> A simpler solution would be:
> 
> > x <- c(3,2,0,1,0,2,0,0,1,0,0,0,0,4,1)
> > y <- rep(NA,length(x))
> > y
>  [1] NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA
> > z <- which(x != 0)
> > l <- z - c(1,z[-length(z)])
> > y[z] <- log(x[z]/(l+1))
> > y
>  [1]  1.0986123  0.0000000         NA -1.0986123         NA
> -0.4054651         NA         NA -1.3862944
> [10]         NA         NA         NA         NA -0.4054651
> -0.6931472
> 
> 
> 
> --- On Tue, 3/6/08, Marc Schwartz
> <marc_schwartz at comcast.net> wrote:
> 
> > From: Marc Schwartz <marc_schwartz at comcast.net>
> > Subject: Re: [R] NOT-SO-SIMPLE function!
> > To: "T.D.Rudolph"
> <prairie.picker at gmail.com>
> > Cc: r-help at r-project.org
> > Received: Tuesday, 3 June, 2008, 5:59 AM
> > on 06/02/2008 01:30 PM T.D.Rudolph wrote:
> > > I am trying to set up a function which processes
> my
> > data according to the
> > > following rules:
> > > 
> > > 1. if (x[i]==0) NA
> > > 2. if (x[i]>0) log(x[i]/(number of consecutive
> > zeros immediately preceding
> > > it +1)) 
> > > 
> > > The data this will apply to include a variety of
> whole
> > numbers not limited
> > > to 1 & 0, a number of which may appear
> > consecutively and not separated by
> > > zeros.  Below is an example with a detailed
> > explanation of the output
> > > desired:
> > > 
> > > x <- c(3,2,0,1,0,2,0,0,1,0,0,0,0,4,1) 
> > > output desired = c(1.098, 0.69, NA, -0.69, NA,
> -0.41,
> > NA, NA, 1.098, NA, NA,
> > > NA, NA, -0.22, 0) 
> > > 
> > > the 1st element, 3, becomes log(3) = 1.098612 
> > > the 2nd element, 2, becomes log(2) = 0.6931472 
> > > the 3rd element, 0, becomes NA (cannot log zero).
> 
> > > the 4rd element, 1, becomes log(1/(1(number of
> > consecutive zeros immediately
> > > preceding it) + 1 (constant))) = log(1/2) = 
> > -0.6931472 
> > > the 5th element, 0, becomes NA 
> > > the 6th element, 2, becomes log(2/(1(number of
> > consecutive zeros immediately
> > > preceding it) + 1 (constant))) = log(2/3) =
> -0.4054651
> > 
> > 
> > The above should be log(2/2) = 0
> > 
> > There is only 1 consecutive zero preceding the 2 in
> the 6th
> > position
> > 
> > > the 7th and 8th elements, both zeros, become NA 
> > > the 9th element, 1, becomes log(1/(2(number of
> > consecutive zeros immediately
> > > preceding it) + 1 (constant))) = log(1/3) = 
> 1.098612 
> > 
> > The above should be log(1/3) = -1.098612 (negative,
> not
> > positive)
> > 
> > > the 10-13th elements, all zeros, each become NA 
> > > the 14th element, 4, becomes log(4/(4(number of
> > consecutive zeros
> > > immediately preceding it) + 1 (constant))) =
> log(4/5)
> > = -0.2231436 
> > > the 15th element, 1, becomes log(1) = 0 
> > > 
> > > This one has been in the works for some time and
> I
> > can't quite seem to crack
> > > it.
> > > I would be indebted to anyone who could with
> success -
> > it seemed so simple
> > > at the offset!
> > > Tyler
> > 
> > I am presuming that you have some typos/errors above
> in
> > your per element 
> > explanation of the processing of the vector.  If so,
> then
> > the following 
> > should work as a first pass and could probably be
> optimized
> > further:
> > 
> > zeroes <- function(x, i)
> > {
> >    if (x[i] == 0) {
> >      NA
> >    } else if (i == 1) {
> >      log(x[i])
> >    } else if (x[i - 1] != 0) {
> >      log(x[i])
> >    } else {
> >      rz <- rle(x[1:(i-1)])
> >      log(x[i] / (rz$lengths[length(rz$lengths)] + 1))
> >    }
> > }
> > 
> > 
> > x <- c(3, 2, 0, 1, 0, 2, 0, 0, 1, 0, 0, 0, 0, 4, 1)
> > 
> > 
> >  > sapply(seq(along = x), function(i) zeroes(x, i))
> >   [1]  1.0986123  0.6931472         NA -0.6931472     
>   
> > NA  0.0000000
> >   [7]         NA         NA -1.0986123         NA     
>   
> > NA         NA
> > [13]         NA -0.2231436  0.0000000
> > 
> > 
> > See ?rle for more information on the identification of
> the
> > sequential 
> > zeroes in the vector.
> > 
> > HTH,
> > 
> > Marc Schwartz
> > 
> > ______________________________________________
> > R-help at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> > http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained,
> > reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained,
> reproducible code.