R function for percentrank

"tom soyer" <tom.soyer at gmail.com> wrote in

John,

The Excel's percentrank function works like this:

if one has a number,

x for example, and one wants to know the

percentile of this number in

a given data set, dataset, one would type

=percentrank(dataset,x) in

Excel to calculate the percentile. So for example,

if the data set is

c(1:10), and one wants to know the percentile of

2.5 in the data set,

then using the percentrank function one would get

0.166, i.e., 2.5 is

in the 16.6th percentile. 

I am not sure how to program this function in R. I

couldn't find it as

a built-in function in R either. It seems to be an

obvious choice for

a built-in function. I am very surprised, but

maybe we both missed it.
 
My nomination for a function with a similar result
would be ecdf(), the 
empirical cumulative distribution function. It is of
class "function" so 
efforts to index ecdf(.)[.] failed for me.

df4$V2

[1] 1 1 1 1 1 5 6 7 9

ecdf.V2<-ecdf(df4$V2)
ecdf.V2(df4$V2)

 [1] 0.2 0.2 0.4 0.4 0.5 0.6 0.7 0.8 1.0 0.9

Don't have Excel, but the OpenOffice.org Calc
program has the same 
function. It produces:
x    percentrank(x)
1	0.0000000
1	0.0000000
3	0.2222222
3	0.2222222
4	0.4444444
5	0.5555556
6	0.6666667
7	0.7777778
10	1.0000000
9	0.8888889

(Not that I am saying that the OO.o/Excel function
is what one _should_ 
want. Its behavior seems pathological to me.)

-- 
David Winsemius

On 12/1/07, John Kane <jrkrideau at yahoo.ca> wrote:

I don't see one but that means nothing.   I think

you

can write such a function in a few minutes

Will something like this work or am I
missunderstanding what Excel's percentrank does ?

aa <- rnorm(25);  aa  # data vector
percentrank <- function(x) {
var  <- sort(x)
p.rank <- 1:length(var)/length(var)*100
dd  <- cbind(var,p.rank)
}
pr <- percentrank(aa); pr


--- tom soyer <tom.soyer at gmail.com> wrote:

Hi,

Does anyone know if R has a built-in function

that

is equvalent to Excel's
percentrank, i.e., returns the rank of a value

in a

data set as a percentage
of the data set?

Thanks,