[R] How to obtain a mean by more than one other variable

[Andrew Koeser]

One function I like is from package psych.

library(psych)
describe.by(ARK$TotalWater, group=Tray:Pot)

Andrew Koeser

On 3/9/2014 10:39 PM, Erynn Call wrote:
> I'm trying to create a new variable (meanABUNDHA) by obtaining a mean value
> *by* other variables.  I surveyed birds (multiple species) at multiple sites
> and have multiple surveys within a REP (i.e. in example data below, SURVEY
> 55 and 57 are in REP 11).  I need the mean ABUNDHA (pooling SURVEY) for each
> BIRD species by REP and by SITE. Below, I would average 0.77 and 0.15 for
> MALL in REP 11 at SITE 1 to get 0.46 meanABUNDHA.
>
> An example of my data are as follows, including the new variable I hope to
> create meanABUNDHA:
> SITE    REP     SURVEY  BIRD    ABUNDHA meanABUNDHA
> 1       11            57             MALL      0.77            0.46
> 1       11            55             MALL      0.15            0.46
> 1       12            58             MALL      0.14            0.14
> 1       2              58             BAEA     0.03            0.03
> 3       4              64             AMCR     0.22            0.45
> 3       5              65             AMCR     0.67            0.45
> 7       11             56             MALL      0.01            0.01
>
> I'm not sure how to incorporate more than one "by="?
>
> data.all4[,mean(ABUNDHA),by=
> REP]
>
> #Add new column containing the by-REP mean of ABUNDHA
> data.all5<-data.all4[,ABUNDHAmean:=mean(ABUNDHA),by=REP]
>
> Thank you for any guidance!!
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.


-- 
Andrew Koeser, BCMA, Ph.D.
Assistant Professor of Landscape Management
University of Florida - Gulf Coast Research and Education Center
813-633-4150