From: Marc Schwartz <marc_schwartz_at_comcast.net>

Date: Mon, 02 Jun 2008 14:59:35 -0500

}

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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. Received on Mon 02 Jun 2008 - 21:12:09 GMT

Date: Mon, 02 Jun 2008 14:59:35 -0500

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

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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. Received on Mon 02 Jun 2008 - 21:12:09 GMT

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