# [R] cumulative growth rates indexed to a common starting point over n series of observations

Dirk Eddelbuettel edd at debian.org
Fri Sep 1 23:07:35 CEST 2006

```On 1 September 2006 at 14:59, Dirk Eddelbuettel wrote:
|
| On 1 September 2006 at 14:30, toby_marks at americancentury.com wrote:
| | The apply with the cumprod was exactly what I was after.  The apply just
| | wasn't clicking with me, and I had overlooked the cumprod.  Thanks to all
| | for pushing me down the right path!
| |
| | Actually, what I am ultimately after is a way to link this series, without
| | having to use a for loop ( the only way I can think of ... ).  But, would
| | like to see if it can be linked  using mapply or apply against the rows
| | and to compute the linked results.
| |
| | zz = matrix(rnorm(20), ncol=2)
| | zzcum = apply(zz/100 + 1, 2, cumprod)
| | Is there a better way here ?
|
| Sure, why not call apply again?
|
| > set.seed(42); zz <- matrix(rnorm(20), ncol=2)
| > zzcum <- apply(1+zz/100, 2, cumprod)
| > apply(rbind(c(1,1), zzcum), 2, cumprod)*100

Small mistake, that compounds twice. You probably want

> set.seed(42)
> zz <- matrix(rnorm(20), ncol=2)
> apply( rbind(c(1,1), zz/100+1), 2, cumprod)*100
[,1]      [,2]
[1,] 100.0000 100.00000
[2,] 101.3710 101.30487
[3,] 100.7985 103.62135
[4,] 101.1645 102.18220
[5,] 101.8048 101.89732
[6,] 102.2163 101.76147
[7,] 102.1079 102.40863
[8,] 103.6512 102.11753
[9,] 103.5531  99.40482
[10,] 105.6433  96.97888
[11,] 105.5770  98.25911
>

Hth, Dirk

--
Hell, there are no rules here - we're trying to accomplish something.
-- Thomas A. Edison

```