Relase positive with log and zero of negative with 0

G'day Kevin,

On Sun, 15 Nov 2009 7:18:18 -0800

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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