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!!
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