[R] data vector to corresonding percentile ranks

[David Winsemius]

On Dec 23, 2011, at 10:28 AM, Steve Jones wrote:

> I have a problem where I need to calculate the corresponding cohort
> percentile ranks for each of several variables.
>
> Essentially, what I need is a function that will calculate the
> distribution-free percentiles from each variable's data vector,  
> returning a
> corresponding vector of percentiles:
>
> e.g.:
>
> percentile.my.data<-/function/(my.data)
>
>
> I tried to make ecdf() perform this task but was unsuccessful.

Unsuccessful? How? Seems like a reasonable strategy:

set.seed(123)
  x <- rnorm(1000)
xCdist <- ecdf(x)

Seems to give sensible results.

 > x[1]
[1] -0.7104066
 > 100*xCdist(x[1])
[1] 23.4

 > x[2]
[1] 0.2568837
 > 100*xCdist(x[2])
[1] 60
>
> I'd be grateful for any help or advice...

My advice would be to post what code you were trying so that you can  
get help understand what difficulties you need to overcome.

-- 

David Winsemius, MD
West Hartford, CT