Re: running cumulative product

["Jordan, Paul" <paul.jordan@roche.com>]

Hi John,

 

try:

 

x[-length(x)]*x[-1]

 

Have Fun!

Paul

---

From: John Pitchard [mailto:johnpitchard@googlemail.com]
Sent: Tuesday, February 19, 2008 12:48 PM
To: s-news@lists.biostat.wustl.edu
Subject: running cumulative product

 

Dear All,

I want to produce a running cumulative product. For example, if I have

 

x <- seq(0.1, 2, 0.1)
> x
 [1] 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0
 

 

Then I want a sequence taking each pair of numbers, i.e. 0.1 and 0.2 (calculate the product), 0.2 and 0.3 (calculate the product), 0.3 and 0.4 (calculate the product),..., 1.9 and 2.0 (calculate the product). So I get a vector of length 18 in this example (20 -2). The vector will look something like this:

 

0.02  0.06.... 3.8

 

Does anyone know an efficient way to generate this sequence?

 

Many thanks in advance.

Regards,

John