# [R] mean for every quartile

chalabi.elahe at yahoo.de chalabi.elahe at yahoo.de
Mon May 16 15:46:06 CEST 2016

```Thnaks for your reply,

By using tapply I get this result:

tapply(df\$BR, findInterval(df\$BR, quantile(df\$BR)), mean)
1   3   4   5
256 320 384 512

But I think this is not true,cause I have to get 5 means but here I get four numbers!

On Monday, May 16, 2016 6:29 AM, Michael Dewey <lists at dewey.myzen.co.uk> wrote:
Dear Elahe

In line

On 16/05/2016 13:31, ch.elahe via R-help wrote:
> Hi all,
> I have a column in my df and I want to get quartiles for this column and then calculate mean for each and every quartile, here is my column:
>

The quartiles are strictly speaking the boundaries but if you really
meant that the problem is trivial so i assume you want to cut the
variable at the quartiles.

>
>     df\$BR
>     [1] 384 384 384 384 512 384 384 320 320 320 320 320 320 320 320 320 320 384
>     [19] 384 384 320 320 320 320 384 384 256 320 320 320 384 320 320 320 384 384
>     [37] 320 320 320 320 320 320 320 320 320 384 320 320 320 320 320 320 384 320
>     [55] 320 320 320 320 320 320 384 512 320 320 320 320 320 320 320 384 384 320
>     [73] 320 320 384 320 320 320 320 256 320 320 384 320 384 320 384 320 320 320
>     [91] 384 320 320 320 320 320 320 320 320 320 320 320
>
> I do the following to get the quartiles:
>
>
>     quantile(m\$BR)
>     0%  25%  50%  75% 100%
>     256  320  320  368  512
>
> now how can I get mean for each quartile?

How about setting up a vector which takes the values 1, 2, 3, 4
depending on the values of BR with cutpoints defined by
quantile(BR)(using ifelse) and then using tapply?

> Thnaks for any help,
> Elahe
>
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