I have this plot, which calculates an index of abbundance of a bird species for a given winter:
This graphic comes from this code (themes and scales excluded):
ggplot (a, aes (pentada,ika,colour=inv,group=inv,na.rm=T)) + geom_line()+
facet_wrap(~inv, ncol=3)+labs(title="SYLATR\n",x="",y="IKA")
and the data frame has 6 variables:
pentada / censos / yr / total / inv / ika
The thing is that I would like to add a line in each of the wintering seasons that shows the mean of the abbundance for all the years combined and I don't know how. should I append the mean as a new column after every wintering season? In this case, how should I do it?.
Thank you.