[R] OT: computing percentage changes with negative and zero values?
Jim Lemon
jim at bitwrit.com.au
Wed Feb 17 12:13:42 CET 2010
On 02/17/2010 04:06 AM, Liviu Andronic wrote:
> Dear all
> I need to compute percentage changes of my data, but unfortunately
> they contain both negative and zero values, and I am quite confused on
> how to proceed. Searching the internet I found that many people ran
> into similar issues, with no obvious solution available.
> ...
> As you have noticed, I'm quite unsure on how to proceed. My actual
> data represents financial EPS (earnings per share) forecasts, ranging
> from -1 to 5. So, it has a "natural zero point" (see David Winsemius'
> comments in [2]). However, I need to compute percentage variations
> since I am primarily interested in the evolution of the forecasts (for
> a given company), while EPS data between two companies are not
> necessarily comparable. The percentage data would subsequently be used
> in performing statistical analyses (regression, etc.).
>
Hi Liviu,
My understanding of percentage change is the absolute value of the
change divided by the absolute value of the initial value and the result
multiplied by 100. Thus:
100*abs(diff(x$var))/abs(x$var[1:19])
[1] 283.720930 187.341772 10.144928 100.000000 Inf 52.980132
[7] 212.676056 46.250000 35.042735 6.329114 223.648649 51.912568
[13] 263.636364 150.000000 69.444444 959.090909 167.195767 40.157480
[19] 275.000000
gives me correct values (and the Inf for the fifth value is correct, as
the denominator is zero). My definition might not be the only one, though.
Jim
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