On 25/07/2008, at 5:24 AM, Robert Baer wrote:
I'm trying to calculate the percent change for a time-series
variable.
Basically the first several observations often look like this,
x <- c(100, 0, 0, 150, 130, 0, 0, 200, 0)
and then later in the life of the variable they're are generally
no more
0's. So when I try to calculate the percent change from one
observation to
the next, I end up with a lot of NA/Nan/INF, and sometimes 0's
which is what
I want, in the beginning.
I know I can use x <- na.omit(x), and other forms of this, to get
rid of
some of these errors. But I would rather use some kind of
function that
would by defult give a 0 while dividing by zero so that I don't
lose the
observation, which is what happens when I use na.omit.
Well, this is not an error but proper behavior in the world of math
that I know.
However, to get what you want you could try
x=(100-0)/0
if(!is.finite(x))x=0
x
The foregoing response exemplifies what I think is the ***RIGHT*** way
to answer wrong-headed questions on this list. ``What you want to do
makes no sense, but if you insist on doing it, here's how.''
To my mind, wanting the result of division by zero to be zero *in
general*
is nothing short of idiotic. But if someone wants to impose this
convention
in his or her own calculations, well that's their ``democratic right''.
And Robert Baer clearly and succinctly (and more tactfully than I) makes
this clear.
A similar style of response would have been appropriate in respect of
the
fooferaw that has been going on, on this mailing list on the topic of
``Coefficients of Logistic Regression from bootstrap - how to get
them?''
cheers,
Rolf Turner
######################################################################
Attention:\ This e-mail message is privileged and confid...{{dropped:9}}
______________________________________________
R-help@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.
