find the quantile percentage given a value

Question

I have a data in the t vector and given the data I can get quantile

   t = c(1,2,3,4,5,6,3,2,21,22,23,2,23,4,4,4444)
  quantile(t,c(.3))
3

But I would like to do the opposite

I want provide 3 and have it return the quantile percentage

like somefunction(3,t) and the output is 30%

Is there a function for that?

You are asking for the `ecdf` function, which is offered as the inverse of quantile on the `?quantile` help page. It is returned as a decimal fraction but if you wanted it displayed as a "percentage" then just multiply by 100. (I suspect this is a duplicate.) — IRTFM, Oct 05 '16 at 17:29

Rentrop · Answer 1 · 2016-10-05T21:08:54.820

7

Using the definition of the quantile:

sum(x<=3)/length(x)

gives you: 0.375

Equivalent

f <- ecdf(x)
f(3) #0.375

edited Oct 05 '16 at 21:08

answered Oct 05 '16 at 16:57

Rentrop

score 4 · Accepted Answer · answered Oct 05 '16 at 16:48

4

If x is the vector, and x0 is the value you want to check, we can use

match(x0, sort(x)) / (length(x) + 1)

For your example:

x <- c(1,2,3,4,5,6,3,2,21,22,23,2,23,4,4,4444)
match(3, sort(x)) / (length(x) + 1)
# [1] 0.2941176

answered Oct 05 '16 at 16:48

Zheyuan Li

2 Answers2