data(DarterOnt)
str(DarterOnt)
head(DarterOnt)
op <- par(mfrow=c(1,2),pch=19)
plot(tl~age,data=DarterOnt,subset=river=="Salmon",main="Salmon R.")
plot(tl~age,data=DarterOnt,subset=river=="Trent",main="Trent R.")
par(op)
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