[R] Getting the index of specific quantiles

[William Dunlap]

You might try something like
   x <- c(9,9,1,3,2,7,6,10,5,6)
   p <- (0:4)/4
   order(x) [ quantile(seq_along(x),p, type=1) ]
   # [1] 3 4 7 1 8
Selecting which value of 'type' works makes my head hurt.
You could also use 1+(p*(length(x)-1) as the index into order(x).


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Nov 22, 2016 at 4:21 AM, Matteo Richiardi <
matteo.richiardi at gmail.com> wrote:

> Dear R-users,
> a very easy one for you, I guess. I need to extract the indexes of the
> elements corresponding to different quantiles of a vector. When a
> quantile is an interpolation between two adjacent values, I need the
> index of the value which is closer (the lower value - or the higher
> value for what matters - in case the quantile is exactly half way
> through).
>
> This is an example.
>
> > x <- c(9,9,1,3,2,7,6,10,5,6)
> > quantile(x)
>   0%  25%  50%  75% 100%
>  1.0  3.5  6.0  8.5 10.0
>
> What I need is a vector 'index' which looks like
>
> > index
> 3   4   7   1   8
>
> Many thanks for your help ! Matteo
>
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