[R] Getting the index of specific quantiles

[David Winsemius]

> On 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
> 

Try this (calculate distances with `outer` and then sweep the columns with `apply`)

> dqt <- outer(x, quantile(x), function(x,y) sqrt( (x-y)^2) )
> apply(dqt, 2, which.min)
  0%  25%  50%  75% 100% 
   3    4    7    1    8 

-- 
David.
> Many thanks for your help ! Matteo
> 
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David Winsemius
Alameda, CA, USA