[R] Quantiles of a subset of data

Pete Brecknock Peter.Brecknock at bp.com
Tue Feb 19 16:52:59 CET 2013

bradleyd wrote
> Excuse the request from an R novice! I have a data frame (DATA) that has
> two numeric columns (YEAR and DAY) and 4000 rows. For each YEAR I need to
> determine the 10% and 90% quantiles of DAY. I'm sure this is easy enough,
> but I am a new to this. 
>> quantile(DATA$DAY,c(0.1,0.9)) 
> 10% 90% 
>  12  29 
> But this is for the entire 4000 rows, when I need it to be for each YEAR.
> Is there no way to use a "by" argument in the quantile function? 
> Thanks for any help you can provide. 
> David

check out

?aggregate or ?by should be of help



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