[R] Relase positive with log and zero of negative with 0

[Berwin A Turlach]

G'day Kevin,

On Sun, 15 Nov 2009 7:18:18 -0800
<rkevinburton at charter.net> wrote:

> This is a very simple question but I couldn't form a site search
> quesry that would return a reasonable result set.
> 
> Say I have a vector:
> 
> x <- c(0,2,3,4,5,-1,-2)
> 
> I want to replace all of the values in 'x' with the log of x.
> Naturally this runs into problems since some of the values are
> negative or zero. So how can I replace all of the positive elements
> of x with the log(x) and the rest with zero?

If you do not mind a warning message:

R> x <- c(0,2,3,4,5,-1,-2)
R> x <- ifelse(x <= 0,0, log(x))
Warning message:
In log(x) : NaNs produced
R> x
[1] 0.0000000 0.6931472 1.0986123 1.3862944 1.6094379 0.0000000 0.0000000

If you do mind, then:

R> x <- c(0,2,3,4,5,-1,-2)
R> ind <- x>0
R> x[!ind] <- 0
R> x[ind] <- log(x[ind])
R> x
[1] 0.0000000 0.6931472 1.0986123 1.3862944 1.6094379 0.0000000 0.0000000

HTH.

Cheers,

	Berwin

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